How to measure the diameter and thread pitch of a bolt?
The thread pitch of a metric thread refers to the distance between two thread crests. The pitch can be measured either with a thread gauge or, if necessary, with a caliper. A thread gauge directly shows the correct pitch. With a caliper, it is advisable to measure the distance over ten crests, which minimizes error compared to trying to measure the distance between two crests directly. Divide the result by ten to determine the thread pitch.
The diameter is measured from crest to crest of the bolt, not from the root of the thread.
Thread charts for M, UNF, and UNC threads.
The table below lists the most common thread sizes and their drill sizes. Some uncommon intermediate sizes have been omitted from the table for readability. You can filter the rows of the table using the "Search" field.
| M | Pitch | Drill size ⌀ [mm] |
|---|---|---|
| M1 | 0,25 | 0,75 |
| M1.1 | 0,25 | 0,85 |
| M1.2 | 0,25 | 0,95 |
| M1.4 | 0,30 | 1,10 |
| M1.6 | 0,35 | 1,25 |
| M1.8 | 0,35 | 1,45 |
| M2 | 0,40 | 1,60 |
| M2.2 | 0,45 | 1,75 |
| M2.5 | 0,45 | 2,05 |
| M3 | 0,50 | 2,50 |
| M3.5 | 0,60 | 2,90 |
| M4 | 0,70 | 3,30 |
| M4 | 0,75 | 3,30 |
| M4.5 | 0,75 | 3,70 |
| M5 | 0,80 | 4,20 |
| M5 | 0,75 | 4,20 |
| M5 | 0,90 | 4,20 |
| M5.5 | 0,90 | 4,60 |
| M6 | 1,00 | 5,00 |
| M7 | 1,00 | 6,00 |
| M8 | 1,25 | 6,80 |
| M9 | 1,25 | 7,80 |
| M10 | 1,50 | 8,50 |
| M11 | 1,50 | 9,50 |
| M12 | 1,75 | 10,20 |
| M14 | 2,00 | 12,00 |
| M16 | 2,00 | 14,00 |
| M18 | 2,50 | 15,50 |
| M20 | 2,50 | 17,50 |
| M22 | 2,50 | 19,50 |
| M24 | 3,00 | 21,00 |
| M27 | 3,00 | 24,00 |
| M30 | 3,50 | 26,50 |
| M33 | 3,50 | 29,50 |
| M36 | 4,00 | 32,00 |
| M39 | 4,00 | 35,00 |
| M42 | 4,50 | 37,50 |
| M45 | 4,50 | 41,50 |
| M48 | 5,00 | 43,00 |
| M52 | 5,00 | 47,00 |
| M56 | 5,50 | 50,50 |
| M60 | 5,50 | 54,50 |
On this page, you will find conversion tables for identifying different threads. The tables currently include M standard/fine threads as well as UNF and UNC threads.
| M fine thread | Drill size ⌀ [mm] |
|---|---|
| M1.6x0.2 | 1,40 |
| M1.8x0.2 | 1,60 |
| M2x0.25 | 1,75 |
| M2.2x0.25 | 1,95 |
| M2.5x0.35 | 2,15 |
| M3x0.35 | 2,65 |
| M3.5x0.35 | 3,15 |
| M4x0.35 | 3,65 |
| M4x0.5 | 3,50 |
| M4.5x0.75 | 3,75 |
| M4.5x0.5 | 4,00 |
| M5x0.5 | 4,50 |
| M5.5x0.5 | 5,00 |
| M6x0.75 | 5,20 |
| M6x0.5 | 5,50 |
| M7x0.5 | 6,50 |
| M7x0.75 | 6,20 |
| M8x0.50 | 7,50 |
| M8x0.75 | 7,20 |
| M8x1 | 7,00 |
| M9x0.75 | 8,20 |
| M9x1 | 8,00 |
| M10x0.75 | 9,20 |
| M10x1 | 9,00 |
| M10x1.25 | 8,80 |
| M11x0.75 | 10,20 |
| M11x1 | 10,00 |
| M12x0.75 | 11,20 |
| M12x1 | 11,00 |
| M12x1.25 | 10,80 |
| M12x1.5 | 10,50 |
| M13x1 | 12,00 |
| M13x1.5 | 11,50 |
| M14x0.75 | 13,20 |
| M14x1 | 13,00 |
| M14x1.25 | 12,80 |
| M14x1.5 | 12,50 |
| M15x1 | 14,00 |
| M15x1.5 | 13,50 |
| M16x1 | 15,00 |
| M16x1.25 | 14,80 |
| M16x1.5 | 14,50 |
| M17x1 | 16,00 |
| M17x1.5 | 15,50 |
| M18x1 | 17,00 |
| M18x1.5 | 16,50 |
| M18x2 | 16,00 |
| M20x1 | 19,00 |
| M20x1.5 | 18,50 |
| M20x2 | 18,00 |
| UNC thread | Drill size ⌀ [mm] |
|---|---|
| 1-64 | 1,50 |
| 2-56 | 1,80 |
| 3-48 | 2,00 |
| 4-40 | 2,30 |
| 5-40 | 2,60 |
| 6-32 | 2,85 |
| 8-32 | 3,50 |
| 10-24 | 3,90 |
| 12-24 | 4,50 |
| 1/-4-20 | 5,20 |
| 5/16-18 | 6,60 |
| 3/8-16 | 8,00 |
| 7/16-14 | 9,40 |
| 1/2-13 | 10,75 |
| 9/16-12 | 12,25 |
| 5/8-11 | 13,50 |
| 3/4-10 | 16,50 |
| 7/8-9 | 19,50 |
| 1-8 | 22,25 |
| 1 1/8-7 | 25,00 |
| 1 1/4 - 7 | 28,25 |
| 1 3/8 - 6 | 30,75 |
| 1 ½ - 6 | 34,00 |
| 1 3/4 - 5 | 39,50 |
| 2 - 4,5 | 45,25 |
| UNF threads | Drill size ⌀ [mm] |
|---|---|
| 1-72 | 1,6 |
| 2-64 | 1,9 |
| 3-56 | 2,1 |
| 4-48 | 2,4 |
| 5-44 | 2,7 |
| 6-40 | 3 |
| 8-36 | 3,5 |
| 10-32 | 4,1 |
| 12-28 | 4,7 |
| 1/4"-28 | 5,5 |
| 5/16"-28 | 6,9 |
| 3/8"-24 | 8,5 |
| 7/16"-20 | 9,9 |
| 1/2"-20 | 11,5 |
| 9/16"-18 | 12,9 |
| 5/8"-18 | 14,5 |
| 3/4"-16 | 17,5 |
| 7/8"-14 | 20,25 |
| 1"-12 | 23,25 |
| 1 1/8"-12 | 26,5 |
| 1 1/4"-12 | 29,5 |
| 1 3/8"-12 | 32,5 |
| 1 ½"-12 | 36 |
| 1"-14 | 23,4 |