web the following table chart defines standard metric external thread size m1 6 to m18 per ansi asme b1 13m 1995 these thread sizes and Bolts are a kind of externally threaded fastener used with a nut. It has a pitch thread of 1.00mm for fine and 1.25mm for standard. A bolt size chart describes its size based on its proportions. The second chart below is a US fraction to metric mm for the more common sizes up to 4". These marks are radial lines; the more lines on the bolt, the greater its strength. Bolts Types and Sizes: Metric & Imperial Bolt Dimensions Chart | CNCLATHING, Thread Types, Terms, Designation, and How to Identify & Measure Threads | CNCLATHING, Different Types of Screws and Their Uses Understanding Wood Screws, Machine Screws and More | CNCLATHING, What is Thread Milling & How Does a Thread Mill Work | How to Thread Mill | CNCLATHING, Thread Sizes (Dimensions) Explained Imperial & Metric Thread Sizes Chart | CNCLATHING, Machine Screw Diameters Chart and Unified National Thread Sizes What is a Machine Screw | CNCLATHING, Guide to Design and Machining Thread: How to Cut an Internal & External Thread? Working out which of the variously sized and shaped bolts in front of you is the one you need can be quite daunting. The diameter and length of the stud and bolt are covered in flange standard ASME B16.5 & B16.47. For instance, you can see the following in the chart: 1 1/8 converts to a 28.575 mm socket. For any other types that are not countersunk, measure from the flat underside to the tip. However, metric bolt head size is measured in millimeters. " Drive. US Wood Screws - Nominal Sizes - Wood screws - nominal sizes vs. diameters. If the head is flat, it will most likely sit flush. They are represented in an alphanumeric code, which is difficult to understand if you are not familiar with it. Let's Fix! It comes in several thread pitches, such as 12-24 and 10-32. It is recorded in a decimal point of an mm. It was introduced in the British Weights and Measures Act of 1824. Structural wood screws have an unthreaded shaft and coarse threads. 12 tips to prevent Denver & Colorado Springs altitude sickness, Why are my car and engine leaking oil? In wrench sets, they will be all positioned in order from smallest size to largest. Bolt heads have three essential dimensions: size across the flats, across the corners, and head height. Thats why we have an additional column in the metric chart below: the Standard Inch Equivalent. This International Standard specifies selected sizes for screws, bolts and nuts in the diameter range from 1 mm to 64 mm of ISO general purpose metric screw threads (M) having basic profile according to ISO 68-1. COARSE THREADS & FINE THREADS Coarse threads are those with larger pitch (fewer threads per axial distance), and fine threads are those with smaller pitch (more threads per axial distance). Use the dimensions of your bolt to determine the appropriate size nut. Do keep note drywall ones cannot support tile and cement board. A #1 gauge is 5/64 inch, and a #2 gauge is 3/32 inch. Metric bolt conversion data forindustrial bolts/rods,machine screwsandsmall diameter fasteners from Raaj Sagar Steels includes metric to standard bolt conversions. My best advice to avoid buying a bolt with the wrong thread pitch is to bring a good bolt from the engine that fits in the bolt hole to your local hardware store for direct comparison. 27 Size Measurements, Measures Thread Sizes, Bolt Lengths in Both inches & Metric Sizes. If you use a bolt smaller than the hole it should go in, the bolt may fall out. The M8 screw size has a diameter of 5/32 inches. A bolt heads diameter depends on its shanks diameter. For example, an M3 bolt with a medium fit would have a 3.4 mm clearance hole. 1. These dimensions are useful when attempting to tighten or loosen a bolt. Whatever the case may be, our wrench conversion chart will give you the best-fitting standard or metric wrench for a given bolt size. | CNCLATHING, Compare Different Fasteners: Difference Between Bolt, Screw, Rivet and Nut | CNCLATHING, What are UNF Threads and UNC Threads? To calculate the gauge and head sizes, you can use the formula below. 9/16. Just make sure youve got a high bolt grade or class. Depending on the application, they come in different forms and sizes. If the bolt body is the same for all bolt types, then the head is the complete opposite. Use a bolt gauge: A bolt gauge is a tool specifically designed for measuring bolt head size. These bolts are the common shiny silver zinc bolts that are used for general purposes. There are also machine bolts with a fully threaded shaft and a semi-cone point, used to fasten wood to wood, wood to metal, and metal to metal. Coarse Thread Sizes Fine Thread Sizes It most likely looks the same for all bolt types. Use the below bolt hole clearance chart for Metric size bolts and screws. It allows you to drill directly into the surface without pre-drilling. Also, you need to show them which standard . As an Amazon Associate we earn from qualifying purchases. Metric bolt sizes are available in a range of diameters, from as small as 2mm to as large as 100mm or more. In our case, only a 1/2 in. Sponsored . So, next time youre working on a project, you can acquire the bolt dimensions that you need easily. When it comes to things as intricate as sizes, knowing the bare minimum helps. On the other hand, bolt torque size charts have many variables and different measurements for each bolt grade/class. The simplest and strongest form of anchor bolt is cast-in-place, another type is post-installed anchors. Then, when you unscrew the bolt, you wont be able to use another bolt in place. The metric thread sizes are generally expressed as M2 0.25, the thread diameter is 2mm and pitch is 0.25mm. If you dont see what youre looking for just call one of our team members at +91-22-6659 5285 Or Mail Usinquiry@raajsagarsteels.com. Pitch: the measurement between the apex of adjacent threads on the bolts shank, equal to the ratio of threads to unit length. Thread pitch can be further described as coarse or standard, fine, or super fine. You can use a multi-material one in several materials, such as drywall or sheet metal. The M12 is even wider and can shoulder heavier loads. For flat-headed ones, measure from the tip to the top to get the length. Use millimeters to measure from one side of a thread to the other. When choosing bolts, you will encounter different sizes and types, and this article will help you select the right size for your construction project. Just like the metric bolt size chart, the metric classes chart has an additional column that contains the standard grade equivalent. The advantage of the metric system is that you can get accurate measurements down to the very smallest increments. To measure screw size, we take its diameter. 8 causes & fixes, Best Portable Air Conditioner Without Hose: Ventless Exhaust Options, What are the dimensions of 70 & 75-inch TVs, 26 Things to Know About Powder Coating: What it is, Colors, How to. Pitch is also described as the number of threads per inch. While almost all bolts have the same body diameter size measurements, there are other dimensions to consider depending on the shape of the bolt. The gauge indicates the diameter. Metric Imperial; Millimetres (mm) This is where tremendously rewarding opportunities come into play. 2. If there are four thread gaps in a one-inch length, the thread pitch would be 0.250 inches (one inch / 4 thread gaps = 0.250 inches). The higher the class number, the greater the bolts strength. It depends on where the head would sit on the surface. Anchor boltWith a threaded part in one end and non-threaded in another end, which can be made in L shape, Pin type, Wedge type, or other forms, often work with steel plates or stiffeners to connect structural and non-structural elements to the concrete, transfer tension forces and shear forces. U-bolts can be made from various materials, durable and non-corrosive metal is the first choice, such as 316 stainless steel, 304 stainless steel, and plain carbon steel. A bolts head is can be round, hexagonal, or square in shape. These parts are standard across all bolt types and consist of the head and body. These selected sizes are recommended also for general engineering use. To get this final measurement, use a ruler or measuring tape. When getting the length using inches, here are some points to keep in mind: Take the diameter by measuring the threads width in fractions of an inch using a measuring tape or ruler. It has a diameter of 10mm and comes in several lengths. No inquiry is too large or too small, we specialize in locating hard to find items. U-boltA U-bolt is in the shape of the letter U with threads on both ends, its typical use is to support/clamp pipes through which fluids and gasses pass, and hold ropes together. fastenerdata makes no warranties or representations regarding . Now the wider applications of U bolts including clamp any kind of tubing/round bar. Keep in mind that when I say bolt size, I refer to the bolts shank, not the head. The thread pitch is the distance between each thread in mm. How to Tighten Your Door Handle Quick & Easy! Phillips and slotted drives are the two main types. These standards dictate things like thickness and screw thread. It helps in fastening wood pieces together. Coarse-threaded ones have a wider space between threads. Now that weve covered all the technical aspects of a bolt size chart, lets look at an example to cement this information. On the other hand, wood deck ones have an unthreaded shank and a coarse-threaded portion. Start measuring wherever the head would rest when fully embedded into something. You can also screw bolts on two different materials, such as fastening wood to metal. Hex bolts are designed with a hexagonal head that to be driven by a wrench and external machine threads, maybe partially threaded or fully threaded. Junying Metal Manufacturing has developed high-level manufacturing technique in That figure also refers to the bolts diameter. A bolt size chart describes its size based on its proportions. A concrete screw is what you need for fastening concrete. US to Metric Conversion Table Print this page . You can use the same method to read a metric chart, but keep in mind that all measurements are in millimeters. The second column has the tensile strength of each grade measured in PSI, followed by the yield strength in the third column. The measurement should start wherever the head rests. Take your time, dont force anything and start threading your bolts with your fingers, they shouldnt be hard to turn at first. Standard Thread Size Tap Drill Size (Inches) Clearance Drill Size (Inches) #0-08 #56 (0.046) 1/16 (0.062) #1-64 #53 (0.059) #49 (.073) #1-72 #53 (0.059) #49 (.073) . document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Copyright 2023 HomeRepairGeek.com - All rights reserved. Flange boltThe flange bolt has a circular flange under the head that acts like a washer to distribute the load. Raaj Sagar Steels is an international supplier of Slotted Machine Screws, Spanner (Snake Eye) Machine Screws, Stainless Steel Lag Screws, Torx Machine Screws, Trim Head Hex Cap Screws, Stainless Steel Wood Screw, One Way Machine Screws.The Screws manufactured in Stainless Steel and Duplex steel, we also manufacture Phillips Machine Screws at our other factory in Vapi, Gujarat. For general use and DIY projects, grade 8 bolts are the strongest options available. To use a caliper, place the bolt head between the jaws of the caliper and carefully adjust the caliper until it fits snugly around the bolt head. Machine screws are fully threaded, which you can use in fastening metal pieces together. Download the Metric Clearance Hole Chart to save the chart as a PDF - useful to print out to have next to your tools. 7/8. If you work with small engines long enough, you will eventually encounter a broken or missing bolt. THREAD (BOLT THREADS) A raised, helical rib or ridge around the interior or exterior of a cylindrically shaped object. Its point will not be chamfered or rounded. Say, youve drilled a 33/64 inches hole, then 33 divided 64 is 0.515625 inches. In general, smaller fasteners have finer threads, so the thread count is higher. Based on the results, the metric bolt size chart shows that you can fit an M14 bolt into the 13mm hole. Metric fasteners are measured by length and pitch, or the distance between threads. When it comes to choosing the right socket, make sure you get the size that suits your drive size. The sixth column in both charts is the second most essential bolt dimension. Bolt Size Bolt Dia. Using a bolt with the right sizes is vital for jobs in various machinery and equipment. A bolts thread pitch in the imperial system is described as a measure of the number of threads it has per inch, while in the metric system, it is described as the distance between two adjacent threads. The head diameter of elevator bolts is larger than other types, which can prevent the bolt from going through soft conveyor material. No inquiry is too large or too small, we specialize in locating hard to find items. That said, its common to see abbreviated metric bolt formats, such as M14-50. For example, 4.0 x 50 means the screw has a diameter of 4 mm and a length of 50 mm. In the standard chart, a bolts tensile strength is represented as grade radial marks on top of the bolts head. 3mm threads are most all .5 (point 5) pitch. Metric . Carriage bolts are usually used to fasten metal to metal or metal to wood. Metric bolts, however, have super fine thread pitchgranted that only bolts M10 and M12 have super fine thread pitch options. Inch. Metric fasteners are specified with a thread pitch instead of a thread count. Quenched and tempered low carbon boron steel, Quenched and tempered medium carbon alloy steel with additives, Quenched and tempered medium carbon steel or carbon steel with additives, Quenched and tempered medium carbon steel, Quenched and tempered low or medium carbon steel, M shows that the bolt uses metric thread, 5 is the bolt shanks nominal diameter in millimeters, 1.0 refers to the thread pitch in millimeters, 20 is the overall length in millimeters, About 0.35 inches of space to keep the bolt flush to the material, Hot-dipped galvanized steel; suitable for outdoor use, Chrome or nickel-plated steel; can be used outdoors, Bronze or brass; expensive and more common in decorative and art pieces. Properly sizing a replacement bolt can be challenging. 4 ways to earn from home by fixing and flipping small engines. The bolt body consists of its shaft with the threaded area. Do you need to take your chances with any bolt that goes in the hole or give up the task altogether? Why is this math lesson necessary, you say. Standard bolt sizes chart pdf The metric system requires new fastener sizes, new material stock sizes, new cutting tools, new gages, etc., to be used in production. This is because the threads are not the same size and will strip or cross thread. If you do see what you are looking, we would love to assist you and give you a quote today! A ruler is all you need to determine thread count and size. The size of a metric bolt is specified using pitch, diameter, and length in millimeters. These are the M Profile limiting Dimensionings . Use a digital caliper or micrometer: Digital calipers and micrometers are more precise measuring instruments that can give you an even more accurate measurement of bolt head size. Thread Pitch But here's the tricky part: In the metric screw chart, the number of threads per inch isn't calculated. Note - Metric screw diameters usually start with "M" (M3, M4, M5. To calculate the wrench size needed, you must first measure your bolt. The cement board type is fully threaded, securing the backer board to subfloors or wall studs. Call our bolting experts at 888-315-0175 with anytorque questions. The number will also tell if a screw can thread through a bolt. Codes such as 1/8-10 x 4/6, M5-0.4 x 15, and 4-30 x 0.10 may seem overwhelming and meaningless at the same time, but it is the most vital information. The metric system is based on millimeters, so metric socket sizes are generally sized like 8mm, 10mm, 12mm, and so on. The maximum tensile strength is 500MPa and the maximum yield strength is 210 MPa. It has a hex head, so you need a socket and ratchet or a wrench to secure it in place. Always refer to project specifications and consult an engineer to ensure that your application is appropriate. For example, in M8-1.0*20, the M means the Metric thread designation, the digit 8 refers to the Nominal diameter (in millimeters), 1.0 refers to the pitch, and 20 refers to the length. Finding the correct size can be a daunting task if you dont know the imperial or metric system. SAE and metric nuts and bolts will need to be used with the corresponding wrench sizes. The most important bolt body dimensions to know include: The bolt diameter is the main size considered and it is measured across the bolt shank or its threaded area. In some cases, you might need to do some conversions if youre working with inches. Tensile Strength (106 Pa) Material Type 4.6 M5 - M36 225 400 Low or medium . Screws are very versatile, making them a popular choice among people. This isnt the only thing thats different, though! A Nut is the counterpart of the Bolt and it is hexagonal (sometimes square) object with threads on the inside. However, metric bolt head size is measured in millimeters. Several kinds of bolts exist, which include Hex bolts, J bolts, T bolts, Anchor bolts, and Flange bolts. And for our international readers, you likely have more metric wrenches in yours. This kind of bolts was used in a carriage which was the basic transportation during inactive times. Strength ratings are as follows- Proof load (max non-deformation): 55,000 psi (33,000 for -1.5") metric-size-chart-hex-bolt Created Date: 2/16/2017 12:47:07 PM . This is why we give the book . 1. Thread pitch refers to how tightly the thread of a bolt goes around the bolt shaft. Metric Bolt Sizes Metric nuts and bolts are commonly referenced using 'M' sizes, for example: M3, M8, M12. These grade marks are given depending on how many pounds per square inch (PSI) the bolt can hold. Hanger bolts feature one side with a self-tapping lag screw thread to grip into the wood, with the other end having machine screw threads to accept a nut or thread into an internally tapped hole. The size of a metric bolt is specified using pitch, diameter, and length in millimeters. To put it simply, this is where the oval top would rest on the surface. So, lets look at some bolt proportions and dimensions. In the USCS imperial system, a bolts tensile strength is usually indicated on its head using grade marks. The thread pitch is the distance between threads expressed in millimetres (measured along the length of the fastener). To determine the correct size u-bolt for your application is important. In other words, the gap in between each thread is 0.250 inches, and it has a Thread Per Inch (TPI) of four. A bolt's size is classified based on a number of dimensions, namely the bolt's diameter, length of shank, thread pitch, grade, thread length and head size. Check the Head Height/Thickness column to ensure that a bolt lays flat to where its screwed. The bolt sizes are labeled differently in the metric size chart. Metric & standard bolt screw sizes are determined by length and thread count. The latter is also commonly referred to as threads per inch (TPI) or thread pitch. More Recent 'Small Engine' Topics on LR Fix, M6 bolt = 10 mm (most common small engine bolt size). Thread sizes for coarse and fine pitch thread were created using the standard sizes from ASME B1.13M. Some are a combination that works for either type. Follow Us. The answer to this question depends on what the bolts will be used on. The bolt chart provides both US and metric stud sizes. In the metric system, its class is indicated via a class number that is imprinted on the bolt head. Instead of using gauges in expressing diameter, the metric system uses millimeters. For example, a bolt and nut may be described as being diameter. Do not use these values for standard metric internal thread design. Flange bolts feature a nozzle, thereby speeding the assembly while eliminating the washer. Instead of the yield strength, the third column contains the tensile strength measured in PSI. This tells you its a metric bolt.Although Metric bolts are measured in millimeters (mm) the M value is a measurement size, not the actual size of the bolt in millimeters. Thread pitch and thread spacing mean the same thing, so dont get those two confused. Coarse threads have a larger threadform relative to screw diameter, whereas fine threads have a smaller threadform relative to screw diameter. Theyre commonly used in automotive applications and construction. There is also the Allen drive, which has a six-sided socket. Different Types of Roof Sheathing and Their Benefits. The M2 screw size has a diameter of 1/16 inch. Sizing for nuts will appear as diameter and pitch. Anchor Bolts are heavy profile hexagon head bolts with full or partial thread configurations. 5.5mm. Shoulder bolts usually used to attach pulleys, moving engine parts, gears, rolling wheels, and stripper plates. The ridge surrounding their heads also makes them easy to be identified. Important: the hexagon sizes shown in the tables should be used as a guide only. Diameter/Decimal/Metric Chart for Small Diameter Fasteners Fastener Conversion Chart 1/4 Drive. Youll find two extra columns: one for Outside Eye Diameter and one for Inside Eye Diameter. The standard metric bolt diameters are specified in the standard ISO 898-1 Tables 4 and 5. Ignition Coil Resistance Chart For 2-Stroke and 4-Stroke Small Engines. Take, for example, eye bolt size charts. Lay-over charts for quickly identifying diameter, thread count and other US fastener dimensions. A larger number means a bigger diameter, whereas a smaller number means a smaller diameter. Thats half a mm between the crest of each thread. The next three columns contain the minimum and maximum sizes across bolt flats, corners, and head height. For metric bolts, head size is measured in millimeters. Lastly, count the threads in one inch to get the thread spacing value. In both charts, theres a minimum and maximum diameter for each bolt. Wood and plastic ones are also good options. How do you convert Metric and Standard? Lastly, the fourth column contains the most common material used in these bolt grades. Below is a table common fastener sizes and lengths and their US (Inch) decimal and closest fraction equivalent. The screw is usually inserted into an existing threaded hole or pass through the material to form its own internal thread, and then it is tightened by applying torque to head. US (inches) Metric (millimeters) 1/16: 1.6: 1/8: 3.2: 3/16: 4.8 The bolt dimension can also be expressed in imperial units. Other types are used for drywall and concrete. SAE J429: The SAE J429 standard is a specification for bolts, screws, and studs that are used in automotive and related industries. Lay it down on a flat surface again. If you dont see what youre looking for just call one of our team members at +91-22-6659 5285 Or Mail Us inquiry@raajsagarsteels.com. Its length is measured from its tip to the point where its shank meets the head. ANSI B1.13M, also identified as ASME B1.13M, defines the standard for metric screw threads in American units with metric units in parenthesis. Dimensional Standards: IS1364, ISO 4014, ISO 4017, DIN 933, DIN 931, BS 1083, BS 1768, ASME B18.2.1, JIS B1180, DIN 558, ISO 4018, DIN-EN14399-4, DIN 601, ISO 4016, CSN 21301, EU 24016, DIN 7968, DIN7990 Size range: Metric: M2 to M42 Inches: 1/4" to 2" Get Quote Hex Bolt Dimensions For example, an 3/8 bolt with a close fit would have a W (0.3860) clearance hole. Hex head ones are an exception to this rule, which means you need to measure from the bottom of the head. The shank has no threads. Download the Imperial Clearance Hole Chart to save the chart as a PDF - useful to print out to have next to your tools.. Want to determine what size clearance hole for Metric, for example, a 10.5 mm clearance hole is required for an M10 close fit, then check out our chart here. Most retailers do not indicate both system sizes on the product page. bolt thats 6 inches or shorter has a 1.25-inch thread length. Handbook of Bolts and Bolted Joints - John Bickford 1998-04-28 Presenting time-tested standard as well as reliable emerging knowledge on threaded fasteners and joints, this book covers how to select parts and materials, predict behavior, control assembly processes, and solve on-the-job problems. RAAJ SAGAR STEELS Address: 163, Dr.M. Use a bolt gauge to find the diameter quickly and easily. Youll notice that they all start with an M followed by a number. All your fastener needs from a single source Aspen Fasteners 4807 Rockside Road, Suite 400, Independence, OH 44131 USA www.aspenfasteners.com | aspensales@aspenfasteners.com | 1-800-479-0056 Boltport is a manufacturer of Anchor Bolts in metric and imperial sizes with coarse, fine, extra fine, and custom threads to various dimensional standards and material specifications. Fine-threaded drywall ones work best with metal studs, while coarse-threaded ones work with wood studs. There are two different methods of sizing wrenches - the standard method (SAE) and the metric sizing. If you often do DIY, one of the popular items you are using is screws. Once you have these values, you can now divide the length by the number of thread gaps. FASTENERS 101 Fastener Reference Tables Conversions, Hardness, Thread Pitch, Tensile Strength The tables below are provided as a general guide to help you better understand metric and imperial measurements. Keep in mind that when purchasing ones with measurements that are listed in the metric system, the initial number is the diameter. Hanger boltHanger bolts are headless bolts with threads on both ends, used to suspend objects from or attach items to wood, it will add an external thread or create a hidden fastening joint. These bolts are usually made from quenched and tempered medium carbon alloy steel, so they can withstand a tremendous amount of pressure. The metric socket size is as follows-. IMPORTANT SCREWS LINKS :Pdf:Dimensions:Faq. The size of a metric screw or bolt is specified as diameter, pitch and length, in millimeters (millimeters is abbreviated "mm"). ANSI B1.13M, also identified as ASME B1.13M, defines the standard for metric screw threads in American units with metric units in parenthesis. Metric Bolt Size Chart Thread Pitch Conclusion Introduction to Bolts, Nuts and Washers A Bolt is a cylindrical object with a hexagonal (sometimes square) head on one end and threads (fully or partially) on the other end. Why? Largest range of all types of bolts and nuts, socket screws, washers, machine screws, rivets, screws, self-drillers, . Individual sizes should be checked before specifying any . bolts fit the bill. Which size bolt will you need to replace it? Ones with a pan, round, or truss head should be measured from the bottom of the head to the tip. Ones with a flat or oval head should be measured from the top to the tip. Still, both terms describe the tensile strength of a bolt, which is the maximum stress it can handle before it snaps. The M10 screw has the widest diameter among these six kinds. The resulting number will be the size of the wrench you need to adjust the bolt properly. A2 and A4 Stainless: This is the class of metric bolts with the A2 and A4 stainless quenched and tempered steel material. Remember that the standard bolt size equivalent is an approximation, not a direct equivalence. Sometimes, they do not know much about it. We use the M2 screw in small items, such as electrical equipment, cameras, and mobile phones. ASME B18.2.1: The ASME B18.2.1 standard is a specification for hex bolts, hex cap screws, and other types of bolts. The metric system was based on the meter, a system of measurement whose origin was in France in the 1970s. Shoulder boltShoulder bolts, also known as shoulder screws or stripper bolts, are a type of machine screws that consist of three sections, the long cylindrical non-threaded shoulder is between the head and threads, which allows the attached part to rotate around or slide along its length. Our Gujarat Division provide total Fasteners Solutions for various projects in India & overseas so far we have supplied Square Drive Pan Head Machine Screws, SS Machine Screw to more than 30 countries like UK, Ireland, Vietnam, Philippines, South Africa, Australia, Kenya, Nigeria, Iran, Russia, Japan, Canada and many more European & African Countries , We have wide range of manufacturing capabilities and due to our proven track record & only 1% rejection rate became Raaj Sagar Steels an ideal choice for major EPC Contractors across the globe for their Steel Fasteners requirements. This column is to help you quickly find the equivalent or approximation of metric bolts. For some time, the imperial system had been the standard measurement system. On the other hand, start from the bottom of the head down to the stem for other types. Its also referred to as the pitch. US Hex Bolts - Metric - ANSI/ASME B18.2.3M Dimensions of Hex Bolts - Metric units. Use this chart to determine the mm size of the M value stamped on a bolt. Here are some of the most common ones. Next, to convert the decimal to millimeters, multiply the decimal by 25.4, which gives you 13.096875mm.