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Thread Pitch Chart: Metric, UNC and UNF Sizes

Thread pitch is the number that sets feed, thread mill path, tap choice and gauge selection, and it is expressed differently in metric and inch work. This chart puts metric coarse, metric fine, UNC and UNF sizes in one table with pitch in millimetres, threads per inch and an approximate thread depth.

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ThreadSeriesMajor dia (mm)Pitch (mm)Threads per inchExternal thread depth (mm)
M3 x 0.5
Metric coarse
3
0.5
50.8
0.3067
M4 x 0.7
Metric coarse
4
0.7
36.2857
0.4294
M5 x 0.8
Metric coarse
5
0.8
31.75
0.4907
M6 x 1
Metric coarse
6
1
25.4
0.6134
M8 x 1.25
Metric coarse
8
1.25
20.32
0.7667
M10 x 1.5
Metric coarse
10
1.5
16.9333
0.9201
M12 x 1.75
Metric coarse
12
1.75
14.5143
1.0734
M16 x 2
Metric coarse
16
2
12.7
1.2268
M20 x 2.5
Metric coarse
20
2.5
10.16
1.5335
M24 x 3
Metric coarse
24
3
8.4667
1.8402
M30 x 3.5
Metric coarse
30
3.5
7.2571
2.1469
M36 x 4
Metric coarse
36
4
6.35
2.4536
M8 x 1
Metric fine
8
1
25.4
0.6134
M10 x 1.25
Metric fine
10
1.25
20.32
0.7667
M12 x 1.25
Metric fine
12
1.25
20.32
0.7667
M12 x 1.5
Metric fine
12
1.5
16.9333
0.9201
M16 x 1.5
Metric fine
16
1.5
16.9333
0.9201
M20 x 1.5
Metric fine
20
1.5
16.9333
0.9201
M24 x 2
Metric fine
24
2
12.7
1.2268
#10-24
UNC
4.826
1.0583
24.0008
0.6492
1/4-20
UNC
6.35
1.27
20
0.779
5/16-18
UNC
7.938
1.4111
18.0001
0.8656
3/8-16
UNC
9.525
1.5875
16
0.9738
1/2-13
UNC
12.7
1.9538
13.0003
1.1985
5/8-11
UNC
15.875
2.3091
11
1.4164
3/4-10
UNC
19.05
2.54
10
1.558
1-8
UNC
25.4
3.175
8
1.9475
#10-32
UNF
4.826
0.7938
31.998
0.4869
1/4-28
UNF
6.35
0.9071
28.0013
0.5564
5/16-24
UNF
7.938
1.0583
24.0008
0.6492
3/8-24
UNF
9.525
1.0583
24.0008
0.6492
1/2-20
UNF
12.7
1.27
20
0.779
5/8-18
UNF
15.875
1.4111
18.0001
0.8656
3/4-16
UNF
19.05
1.5875
16
0.9738
1-12
UNF
25.4
2.1167
11.9998
1.2984

Pitch is the distance between adjacent thread crests. Threads per inch is computed as 25.4 divided by pitch in mm. Thread depth uses the ISO and Unified external thread depth of about 0.6134 times pitch for a rounded root; sharp-V depth is larger and your drawing governs.

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How to use the chart

Search by size or series to jump to the row you need. Metric rows list pitch directly, while inch rows list pitch converted to millimetres so you can compare across systems and program a CNC lathe in a single unit. The threads per inch column is computed from pitch, which is useful when a drawing gives mm and a pitch gauge is marked in TPI. Export the result to Excel to drop a pitch table into a program sheet or tooling document.

  • Filter on UNC or UNF to see inch series
  • Use pitch in mm for G76 or G32 thread cycles
  • Use TPI when reading a pitch gauge

Definitions and conversions

Pitch is the axial distance from one thread crest to the next. For single-start threads, lead equals pitch, so each spindle revolution advances the tool by one pitch. Threads per inch equals 25.4 divided by pitch in millimetres, and the reverse also holds. Coarse series suits general fastening and softer materials, while fine series gives more adjustment resolution and better resistance to loosening in thin walls and vibration environments.

Using pitch in programming

On a lathe, the feed per revolution during threading equals the pitch for a single-start thread, so the pitch in this chart is the F value on a G32 block or the F or E word in a G76 cycle depending on the controller. The thread depth column indicates a starting point for total radial infeed; many programmers apply a small allowance to account for tool nose radius and crest truncation. Always confirm with the controller manual and the drawing tolerance class.

Common mistakes

Frequent errors include confusing 1/2-13 with 1/2-20 when the callout only says 1/2 inch, entering TPI where the control expects pitch in mm, and assuming 24 TPI threads are the same in 5/16 and 3/8 sizes when only the pitch matches. Check both major diameter and pitch before cutting or ordering gauges.

  • Check both diameter and pitch
  • Do not enter TPI in a pitch field
  • Confirm the thread class and hand

Frequently Asked Questions

How do I convert threads per inch to pitch in mm?

Divide 25.4 by the threads per inch. A 20 TPI thread has a pitch of 25.4 divided by 20, which is 1.27 mm. To go the other way, divide 25.4 by the pitch in mm to get threads per inch.

What is the pitch of M10 coarse?

M10 coarse has a pitch of 1.5 mm, and the common fine pitch for M10 is 1.25 mm. The callout M10 x 1.5 includes the pitch, while a plain M10 in most contexts means the coarse pitch.

What is the difference between UNC and UNF?

Both are Unified inch threads with a 60 degree profile. UNC is coarse with fewer threads per inch and UNF is fine with more. For example 1/4-20 is UNC and 1/4-28 is UNF.

Is thread depth the same as thread height?

Not exactly. Basic thread height is about 0.5413 times pitch, while the practical external thread depth with a rounded root is nearer 0.6134 times pitch. The value shown here is the practical depth, so confirm on the drawing.

If thread callouts and tooling live across drawings and an ERP, we can help connect them so planners and machinists see the same data.

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