Size Chart for Bolts and Different Types

Bolts are a type of externally threaded fastener. During assembly, it won’t rotate, but the nut is turned to tighten it. The screw is often placed into an already-existing threaded hole or is passed through the material to create its own internal thread. It is then torqued to tighten the screw (skip straight to the size chart for bolts).

Size Chart for Bolts and Different Types
Photo by Robert Ruggiero on Unsplash

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Jump right into the Frequently Asked Questions

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Size Chart for Bolts Table of Content

Types of bolts

Bolt Size Chart - Bolt Dimensions, Thread, How to measure Bolt Size by bolt type
Bolt Size Chart – Bolt Dimensions, Thread, How to measure Bolt Size by bolt type
  • Elevator bolt; Similar to the carriage bolt but elevator bolt with a thin flat or countersunk head and a square undercut, used in conveyor system setups.
  • Hex bolt: Heavy Hex bolt is designed with a hexagonal head or hex head bolts that are to be driven by a wrench and external machine threads.
  • Lag bolt: Lag bolts, also known as lag screws, are one of the toughest fasteners and are extremely sturdy. This kind of bolt can create its thread and form a friction joint in wood with its coarse threads and other soft materials when tightened.
  • J-bolt: J-bolts are fasteners in the shape of a J with threads in the non-curved area and a hook for support in another section. J-bolts are used in construction and available in various lengths and diameters.
  • U-bolt: A U-bolt has threads on both sides and is shaped like the letter “U,”. The size of the pipe that a U-bolt is clamping might define it. The most durable and non-corrosive metals, such as 316 stainless steel, 304 stainless steel, and plain carbon steel, are used to make U-bolts.
  • Hanger bolt: When used to suspend items. hanger bolts or headless bolts with threads on both ends add an external thread or form a concealed fastening joint.

    Other types of bolts include flange bolts, flat head bolts, sex bolt also known as barrel bolt or connector bolt, square bolts, shoulder bolt, carriage bolt also called coach bolt, eye bolts, and anchor bolt.

Size Chart for Bolts

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Let us now see some bolt size charts. We will see both imperial and metric charts for bolt dimensions and the thread pitch.

Size Chart for Bolts (Imperial)

 Threads Shark diameter Width across flats Head thickness 
Nominal bolt sizeUNCUNFMaxMinMaxMinMaxMin
1/4 mm 0.00985inches20 mm 0.788inches28 mm 1.1inches0.25 mm 0.0099inches  0.246 mm 0.0097inches  0.438mm 0.0172inches0.428 mm 0.0169inches0.163 mm 0.0458inches0.15 mm 0.045inches
5/16 mm 0.012 inches18 mm    0.71 inches24 mm 0.95inches0.3125mm 0.0123inches0.3066 mm 0.012inches  0.5 mm 0.0197inches  0.489 mm 0.0192inches0.211 mm 0.00477inches0.195 mm 0.00768inches
3/8 mm 0.015 inches16 mm 0.63 inches24 mm 0.95 inches0.375 mm 0.0147inches0.369 mm 0.0146inches0.562 mm 0.0221inches0.551 mm 0.0219inches0.243 mm 0.0957 inches0.226 mm 0.089 inches
7/16 mm 0.017inches14 mm 0.55 inches20 mm 0.788inches0.4375 mm 0.0172inches0.4306 mm 0.0168inches0.625 mm 0.0246inches0.612 mm 0.0243inches0.291 mm 0.0114 inches0.272 mm 0.0107 inches
1/2 mm 0.016inches13 mm 0.51 inches20 mm 0.788inches0.5 mm 0.0197inches0.493 mm 0.0194inches0.75 mm 0.0296inches0.736 mm 0.029 inches0.323 mm 0.0127 inches0.302 mm 0.0119 inches
5/8 mm 0.025inches11 mm 0.43 inches18 mm 0.709inches0.625 mm 0.0246inches0.617 mm 0.0243inches0.938 mm 0.0369inches0.922 mm 0.0362inches0.403 mm 0.0158 inches0.378mm 0.0149 inches
3/4 mm 0.03 inches10 mm 0.394inches16mm 0.63 inches0.75 mm 0.0296inches0.741 mm 0.0292inches1.125mm 0.0443inches1.1mm 0.043 inches0.483 mm 0.019 inches0.455 mm 0.0179 inches
7/8 mm 0.034inches9 mm 0.35 inches14 mm 0.55inches0.875 mm 0.044 inches0.866 mm 0.0341inches1.312 mm 0.0517inches1.285 mm 0.05inches  0.563 mm 0.0221inches0.531 mm 0.0209 inches
1 mm 0.394inches8 mm  0.315 inches14 mm 0.55 inches1 mm 0.0394 inches0.99mm   0.0039 inches1.5 mm 0.0591 inches1.469mm 0.0586inches0.627mm 0.0641 inches  0.591 mm 0.0626 inches

Size Chart for Bolts (Metric)

Nominal bolt sizePitch Shark diameter Width across flats Head thickness 
M61 mm 0.0394inches0.75 mm 0.0296inches6 mm 0.2364inches5.82mm 0.23inches10 mm 0.394inches9.78 mm 0.385inches4.15 mm 0.163inches3.85 mm 0.1517inches
M81.25 mm 0.0492inches1 mm 0.0394inches8 mm 0.3152inches7.78 mm 0.307inches13 mm 0.512inches12.73 mm 0.5015inches5.45 mm 0.214inches5.15 mm 0.203inches
M101.5 mm 0.0591inches1.25 mm 0.0492inches10 mm 0.394inches9.78 mm 0.389inches16 mm 0.63 inches15.73 mm 0.6197inches6.58 mm 0.24inches6.22 mm 0.245inches
M121.75 mm 0.0689inches1.25 mm 0.0492inches12 mm 0.4728inches11.73 mm 0.462inches18 mm 0.709inches17.73 mm 0.699inches7.68 mm 0.3026inches7.32 mm 0.288inches
M142 mm 0.0788inches1.5 mm 0.0591inches14mm  0.5516inches13.72 .mm 0.546inches21 mm 0.8274inches20.67 mm 0.8144inches8.98 mm 0.354inches8.62 mm 0.34inches
M162 mm 0.0788inches1.5 mm 0.0591inches16 mm 0.63 inches15.73 mm 0.586inches24 mm 0.9456inches23.67 mm 0.9325inchs10.18 mm 0.401inches9.82 mm 0.387inches
M202.5  mm 0.0985inches  1.5 mm  0.0591inches  20 mm 0.788 inches19.67 mm 0.774inches30 mm 1.182inches29.67 mm 1.167inches12.715mm 0.5inches12.85mm 0.506inches
M243 mm 0.1182inches2mm 0.0788inches24 mm 0.9456inches23.67 mm 0.9325inches36 mm 1.418inches35.38 mm 1.294inches15.22 mm 0.4inches  14.785mm 0.5826inches
Bolt Dimensions | Drill bit sizes, Screws and bolts, Metric bolt sizes
Bolt Dimensions | Drill bit sizes, Screws and bolts, Metric bolt sizes (by Valvers)

Metric clearance and tapping drill hole sizes chart

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SizeClearance HoleThread Pitch (std)Tapping Drill (std Pitch)Thread Pitch (fine)Tapping Drill (fine pitch)
M55.5 mm 0.22 inches0.8 mm 0.0315 inches4.2 mm 0.65 inchesn/ln/l
M66.5 mm 0.27 inches1.0 mm 0.0394 inches5.0 mm 0.197 inches0.75 mm 0.03 inches5.25 mm 0.21 inches
M89 mm 0.35 inches1.25 mm 0.05 inches6.75 mm 0.266 inches1.0 mm 0.0394 inches7 mm 0.276 inches
M1011 mm 0.43 inches1.5 mm 0.06 inches8.5 mm 0.335 inches1.25 mm 0.05 inches8.75 mm 0.45 inches
M1214 mm 0.55 inches1.75 mm 0.069 inches10.25 mm 0.404 inches1.5 mm 0.06 inches10.5 mm 0.41 inches
M1618 mm 0.71 inches2.0 mm 0.08 inches14 mm 0.55 inches1.5 mm 0.06 inches16.5 mm 0.65 inches
M2022 mm 0.87 inches2.5 mm 0.1 inches17.5 mm 0.69 inches1.5 mm 0.06 inches20.5 mm 0.81 inches
M2426 mm 1.02 inches3.0 mm 0.12 inches21 mm 0.827 inches2.0 mm   0.08 inches22 mm 0.87 inches
M3032 mm 1.26 inches  3.5 mm 0.14 inches26.5 mm 1.04 inches2.0 mm 0.08 inches28 mm 1.103 inches

Standard Spanner and Allen Key Sizes Chart

SizeSpannerAllen Key
M58 mm 0.32 inches4 mm 0.16 inches
M610 mm 0.4 inches5 mm 0.2 inches
M813 mm 0.5 inches6 mm 0.24 inches
M1017 mm 0.66 inches8 mm 0.32 inches
M1219 mm 0.74 inches10 mm 0.4 inches
M1624 mm 0.95 inches14 mm 0.55 inches
M2030 mm 1.18 inches17 mm 0.66 inches
M2436 mm 1.42 inches19 mm 0.74 inches
M3046 mm 1.81 inchesn/l
Bolt Size Chart - Different types of dimensions in measuring bolts
Bolt Size Chart – Different types of dimensions in measuring bolts

How to choose the size of the right bolt and what is the best size for you

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Measuring Screws and Bolts (Using Size Chart for Bolts)

Knowing where to look for the diameter and length of the fasteners you need is a crucial first step in getting the right parts.

Diameters of Screws / Bolts

The distance between the outer threads on one side and the outer thread on the other side is used to determine the diameter of screws and bolts. This is known as the main diameter and is usually the bolt’s appropriate size. You can also find the minor diameter from one side to the other of the threads’ bottom hollow.

A number is typically used to identify the size of 1/4″ or less. A nominal measurement is what it’s called. These are the numbers, as well as the decimal equivalents.

Length of Screws / Bolts

The easiest method to remember how to measure length is to use the following formula: The length of a screw or bolt is measured from the flat part of the head to the tip or blunt end. Almost all screw heads are either flat on top or flat on the bottom.

Metric Bolt Measurement Standards

While different standardization, such as DIN, ISO, and JIS, may or may not require different dimensions for their respective bolts, measuring the bolts is generally the same, with only very few exceptions. The rare exceptions generally only affect how they are defined and not necessarily a change in the dimensions themselves. This is clearly seen in some pins.

Other Important Measurements

Some bolts have special features that can be required for proper sourcing. For example, hex head cap screws have a hexagon above the shank. The head itself is often measured by the WAF (width across the flats – the width across the head from one side to the adjacent side).

WAF can differ between standardization, such as between DIN 933 and ISO 4017. At most sizes, there is no difference, but at the M10, M12, M14, and M22 sizes The WAF is slightly different, which can affect its usefulness in some applications.

If you have enjoyed reading this article. On the bolt size, metric bolt measurement standards, and imperial bolt size, please don’t forget to share your experience in the comments section!

Learn more about different types of bolt and bolt sizes (video)

How to Measure Bolts, Nuts and Screws Using a Thread Gauge Size Tool by

Frequently Asked Questions on Size Chart for Bolts

What bolt sizes are specified?

Pitch, diameter, and length in millimeters are used to specify the size of a metric bolt. For example, in M8-1.0*20, “M” stands for Metric thread designation, “8” stands for the nominal diameter (in millimeters), “1.0” stands for pitch, and “20” stands for length.

What do bolt size numbers mean?

The nominal or root (minor) diameter (mm) is the first number in each size, and the thread pitch (mm) is the second number (mm). Keep in mind that the nominal bolt diameter is taken from the bottom of the threads, not the top which would be the major diameter.

What does the M mean in bolt sizes?

The “M” designation for metric screws shows the nominal outer diameter of the screw thread, in millimeters

Is M6 or M8 bigger?

In terms of width, the new M8 is only 0.27 inches wider than the M6. The new BMW M8 is shorter than the M6, with the M8 bolt measuring 53.62 inches and the M6 measuring 54.10 inches.

Does M10 mean 10mm?

M10 means a 10-millimeter outer diameter for the bolt or whatever piece it is.


An overview of bolts, including common bolt materials, numerous types of bolts, and typical bolt specifications and measurements. With the help of illustrations and a Bolt Size Chart, you may also learn about Bolt Size, Bolt Head Size, and their differences. Bolt dimensions and thread pitch are given in the Bolt Size Chart’s imperial and metric units.

Picture in this post is by Edge2Edge Media on Unsplash

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