Here’s a simplified guide to identifying threaded fasteners.
When it comes to identifying fastener sizes,thread is key. Youhave to knowwhen you are dealing with metric or imperial fasteners.From there, you can cross-reference from the table below, which contains data diligently compiled from verified sources.
Metricfastenersusethreadpitch
Thread pitchis the distance from one thread to thenext (adjacent thread).It isexpressed in millimetres.
Metric fasteners aretypicallyprefixed by an M, which makes them easily distinguishable fromimperialfasteners.
Thread patternsare classified aseither coarse (longer) or fine (shorter)pitch.
Americanand Britishfasteners use threadsper inch
ThreadsPerInch(TPI)is the number of threads in an inch.
When dealing with threaded fasteners from North America,you'll referto them inUnified Thread Standard(UTS) thatuse:
Unified National Coarse (UNC)-Coarsethreads*,lowerTPI values
United National Fine (UNF)-Fine threads*,higherTPI values
You mayalsoencounter threaded fastenersfrom the UKthat still use theBritish Standard:
British Standard Whitworth(BSW) -Coarse threads*
British Standard Fine (BSF)- Fine threads*
British Association (BA) - Typically suffixed with BA
*Labeled in fractional inches (eg. 1/8”) based on nominal size
Metric vsImperialequivalents
Refer to this table when cross-referencing your bolt, nut or screw. Not all metricfastenershave imperial equivalents,and vice versa.
| Metric (Pitch inmm) | Unified Thread Standard (Threads Per Inch) | British Standard (Threads Per Inch) | ||||||||
| Size | Coarse(mm) | Fine(mm) | Size | Coarse(UNC) | Fine(UNF) | Size | Coarse (BSW) | Fine (BSF) | BA | |
| -- | -- | -- | -- | #0000 | -- | 160 | -- | -- | -- | -- |
| -- | -- | -- | -- | #000 | -- | 120 | -- | -- | -- | -- |
| -- | -- | -- | -- | #00 | -- | 90 | -- | -- | -- | -- |
| M1.6 | 0.35 | 0.20 | -- | #0 | -- | 80 | -- | -- | -- | -- |
| M2 | 0.40 | 0.25 | -- | #1 | 64 | 72 | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 1/16" | 60 | -- | -- |
| -- | -- | -- | -- | #2 | 56 | 64 | 8BA | -- | -- | 59.1 |
| M2.5 | 0.45 | 0.35 | -- | #3 | 48 | 56 | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 3/32" | 48 | -- | -- |
| -- | -- | -- | -- | #4 | 40 | 48 | 6BA | -- | -- | 47.9 |
| M3 | 0.50 | 0.35 | 1/8” | #5 | 40 | 44 | 1/8" | 40 | -- | -- |
| M3.5 | 0.60 | 0.35 | -- | #6 | 32 | 40 | 4BA | -- | -- | 38.5 |
| -- | -- | -- | -- | -- | -- | -- | 5BA | -- | -- | 43 |
| M4 | 0.70 | 0.50 | -- | #8 | 32 | 36 | 3BA | -- | -- | 34.8 |
| M4.5 | 0.75 | 0.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 2BA | -- | -- | 31.4 |
| M5 | 0.80 | 0.50 | 3/16” | #10 | 24 | 32 | 3/16" | 24 | 32 | 32 |
| M5.5 | -- | 0.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| -- | -- | -- | -- | #12 | 24 | 28 | 1BA | -- | -- | 28.2 |
| M6 | 1.00 | 0.75 | -- | -- | -- | -- | 0BA | -- | -- | 25.4 |
| -- | -- | -- | 1/4" | -- | 20 | 28 | 1/4" | 20 | 26 | -- |
| M7 | 1.00 | 0.75 | -- | -- | -- | -- | 9/32" | -- | 26 | -- |
| M8 | 1.25 | 1.00 | 5/16” | -- | 18 | 24 | 5/16" | 18 | 22 | -- |
| M9 | 1.25 | 1.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M10 | 1.50 | 1.25 | 3/8” | -- | 16 | 24 | 3/8" | 16 | 20 | -- |
| M11 | 1.50 | 1.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| -- | -- | -- | 7/16” | -- | 14 | 20 | 7/16” | 14 | 18 | -- |
| M12 | 1.75 | 1.25 | 1/2" | -- | 13 | 20 | 1/2" | 12 | 16 | -- |
| M14 | 2.00 | 1.50 | 9/16” | -- | 12 | 18 | 9/16" | 12 | 16 | -- |
| M15 | -- | 1.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| M16 | 2.00 | 1.50 | 5/8” | -- | 11 | 18 | 5/8” | 11 | 14 | -- |
| -- | -- | -- | -- | -- | -- | -- | 11/16" | 11 | 14 | -- |
| M17 | -- | 1.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| M18 | 2.50 | 1.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| M20 | -- | 1.50 | ¾" | -- | 10 | 16 | 3/4" | 10 | 12 | -- |
| M22 | 2.50 | 1.50 | 7/8” | -- | 9 | 14 | 7/8” | 9 | 11 | -- |
| M24 | 3.00 | 2.00 | 1” | -- | 8 | 14 / 12 | 1" | 8 | 10 | -- |
| M25 | -- | 2.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M27 | -- | 2.00 | 1 1/8” | -- | 7 | 12 | 1 1/8” | 7 | 9 | -- |
| M28 | -- | 2.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M30 | 3.50 | 2.00 | 1 ¼" | -- | 7 | 12 | 1 ¼" | 7 | 9 | -- |
| M32 | 00 | 2.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M33 | 3.50 | 2.00 | 1 3/8” | -- | 6 | 12 | 1 3/8” | 6 / 7 | 8 | -- |
| M35 | -- | 1.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| M36 | 4.00 | 3.00 | 1 ½" | -- | 6 | 12 | 1 ½" | 6 | 8 | -- |
| M38 | -- | 1.50 | -- | -- | -- | -- | -- | -- | -- | -- |
| M39 | 4.00 | 3.00 | 1 5/8” | -- | -- | -- | 1 5/8” | 5 | 8 | -- |
| M40 | -- | 3.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M42 | 4.50 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M45 | 4.50 | 4.00 | 1 ¾" | -- | 5 | -- | 1 ¾" | 5 | 7 | -- |
| M48 | 5.00 | 4.00 | 1 7/8” | -- | 5 | -- | -- | -- | -- | -- |
| M50 | -- | 3.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M52 | 5.00 | 4.00 | 2” | -- | 4.5 | -- | 2” | 4.5 | 7 | -- |
| M55 | -- | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M56 | 5.50 | 4.00 | 2 ¼" | -- | 4.5 | -- | 2 ¼" | 4 | 6 | -- |
| M58 | -- | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M60 | 5.50 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M62 | -- | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M64 | 6.00 | 4.00 | 2 ½" | -- | 4 | -- | 2 ½" | 4 | 6 | -- |
| M65 | -- | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M68 | 6.00 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M70 | 6.00 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M72 | 6.00 | 4.00 | 2 3/4" | -- | 4 | -- | 2 3/4" | 3.5 | 6 | -- |
| M75 | -- | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M76 | 6.00 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M78 | -- | 2.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M80 | 6.00 | 4.00 | 3” | -- | 4 | -- | 3” | 3.5 | 5 | -- |
| -- | -- | -- | 3 ¼" | -- | 4 | -- | 3 ¼" | 3.25 | 5 | -- |
| M85 | 6.00 | 4.00 | -- | -- | -- | -- | -- | -- | -- | -- |
| M90 | 6.00 | 4.00 | 3 ½" | -- | 4 | -- | 3 ½" | 3.25 | 4.5 | -- |
| -- | -- | -- | 3 ¾" | -- | 4 | -- | 3 ¾" | 3 | 4.5 | -- |
| M100 | 6.00 | -- | 4” | -- | 4 | -- | 4” | 3 | 4.5 | -- |
| -- | -- | -- | -- | -- | -- | -- | 4 1/4" | 2.875 | 4 | -- |
| -- | -- | -- | -- | -- | -- | -- | 4 1/2" | 2.875 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 4 3/4" | 2.75 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 5" | 2.75 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 5 1/4" | 2.625 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 5 1/2" | 2.625 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 5 3/4" | 2.5 | -- | -- |
| -- | -- | -- | -- | -- | -- | -- | 6 | 2.5 | -- | -- |
Tablevalues compiled from:
Hobson Technical Thread Table
Aside from the threadpitch (metric) or count (imperial),other factors to consider when buying fasteners include:
Type(bolt, nut or screw)
Head
Strength(classified by grade/class)
Material and finish (coating)
Tensile properties (low/high tensile)
Thread length (full/partial)
(We’ll cover them in detail in future articles.)
It’s always great to have a sample of the fastener you’re shopping for, but that won’t always be the case.We have a wide range offastener listingswith pictures that you can use for reference.
If in doubt, reach outtous via chat or email and we’ll assistyoupromptly.
