Tap Drill Charts Compared: Starrett, Little Machine Shop and 6 More
We read eight published tap drill charts, from Starrett, two tap makers, a drill maker, three suppliers and a reference site, and lined up their drills for 30 inch threads and the common metric sizes. Every chart lists the same size for only two of the inch threads: 5/16-24 and 1/2-20.
The charts we compared
| Chart | Publisher | Inch threads listed | Drills outside 2B |
|---|---|---|---|
| American Fastener | Fastener supplier | 28 | 2 |
| Little Machine Shop | Tool supplier | 30 | 3 |
| Starrett (Bulletin 1317, a copy hosted by Florida International University) | Tool maker | 28 | 2 |
| Bolt Depot | Fastener supplier | 25 | 6 |
| Engineering Toolbox | Reference site | 28 | 11 |
| Champion Cutting Tool | Tap maker | 28 | 9 |
| Emuge | Tap maker | 30 | 0 |
| Hartner (Gühring group) | Drill maker | 27 | 0 |
Fabworks and Microform Precision print the same inch drills as Little Machine Shop, so they are not repeated. We left out the Machinery's Handbook, because its tables are not free to read online. Every chart was read on 20 October 2026.
Every chart, every inch thread
The standard drill is the one most printed charts give. Each cell shows the drill a chart prints and the thread it leaves by the formula in OSG's chart. Highlighted cells do not include the standard size. "Over 2B" and "under 2B" mark holes outside the class 2B minor diameter limits.
| Thread | Standard drill | American Fastener | Little Machine Shop | Starrett | Bolt Depot | Engineering Toolbox | Champion Cutting Tool | Emuge | Hartner | Charts that differ |
|---|---|---|---|---|---|---|---|---|---|---|
| #0-80 | 3/64 in 81% | 3/64 in 81% | 3/64 in 81% | 3/64 in 81% | 3/64 in 81% | 1.25 mm 66% | #56 83% 3/64 in 81% | 0.0480 in 74% | not listed | 2 of 7 |
| #2-56 | #50 69% | #50 69% | #50 69% | #50 69% | #50 69% | 1.8 mm 65% | #51 82% #50 69% | #50 69% | 1.85 mm 57% | 2 of 8 |
| #4-40 | #43 71% | #43 71% | #43 71% | #43 71% | #43 71% 3/32 in 56% | 2.35 mm 60% | #44 80% #43 71% | #43 71% | 2.35 mm 60% | 2 of 8 |
| #5-40 | #38 72% | #38 72% | #38 72% | #38 72% | #38 72% | 2.65 mm 64% | #39 79% #38 72% | #38 72% | 2.65 mm 64% | 2 of 8 |
| #6-32 | #36 78% | #36 78% | #36 78% | #36 78% | #35 69% 7/64 in 71% | 2.85 mm 64% | #36 78% 7/64 in 71% | #34 67% | 2.85 mm 64% | 4 of 8 |
| #6-40 | #33 77% | #33 77% | #33 77% | #33 77% | not listed | 2.95 mm 67% | #33 77% #32 68% | 3.0 mm 61% | 2.95 mm 67% | 3 of 7 |
| #8-32 | #29 69% | #29 69% | #29 69% | #29 69% | #29 69% | 3.5 mm 65% | 3.4 mm 74% #29 69% | #29 69% | 3.5 mm 65% | 2 of 8 |
| #10-24 | #25 75% | #25 75% | #25 75% | #25 75% | #25 75% 5/32 in 62%, over 2B | 4.0 mm 60%, over 2B | 3.7 mm 82% #25 75% | #24 70% | 3.9 mm 67% | 3 of 8 |
| #10-32 | #21 76% | #21 76% | #21 76% | #21 76% | #21 76% 5/32 in 83% | 4.1 mm 70% | 5/32 in 83% #21 76% | 4.1 mm 70% | 4.1 mm 70% | 3 of 8 |
| #12-24 | #16 72% | #16 72% | #16 72% | #16 72% | #16 72% 11/64 in 82% | 4.65 mm 61%, over 2B | 11/64 in 82% #17 79% | #16 72% | 4.5 mm 72% | 2 of 8 |
| 1/4-20 | #7 75% | #7 75% | #7 75% | #7 75% | #7 75% 13/64 in 72% | 5.35 mm 61%, over 2B | #9 83% #7 75% 13/64 in 72% | #6 71% | 5.1 mm 76% | 2 of 8 |
| 5/16-18 | letter F 77% | letter F 77% | letter F 77% | letter F 77% | letter F 77% 17/64 in 65%, over 2B | 6.8 mm 62%, over 2B | letter F 77% letter G 71% | letter G 71% | 6.6 mm 73% | 3 of 8 |
| 3/8-16 | 5/16 in 77% | 5/16 in 77% | 5/16 in 77% | 5/16 in 77% | 5/16 in 77% | 8.25 mm 62%, over 2B | 5/16 in 77% letter O 73% | letter O 73% | 8.0 mm 74% | 3 of 8 |
| 7/16-14 | letter U 75% | letter U 75% | letter U 75% | letter U 75% | letter U 75% 23/64 in 84%, under 2B | 9.65 mm 62%, over 2B | letter U 75% | letter U 75% | 9.4 mm 73% | 2 of 8 |
| 1/2-13 | 27/64 in 78% | 27/64 in 78% | 27/64 in 78% | 27/64 in 78% | 27/64 in 78% | 11.15 mm 61%, over 2B | 27/64 in 78% 11.0 mm 67% | 27/64 in 78% | 10.8 mm 75% | 2 of 8 |
| 9/16-12 | 31/64 in 72% | 31/64 in 72% | 31/64 in 72% | 31/64 in 72% | 31/64 in 72% | 12.6 mm 61%, over 2B | 15/32 in 87%, under 2B 31/64 in 72% | 31/64 in 72% | 12.2 mm 76% | 2 of 8 |
| 5/8-11 | 17/32 in 79% | 17/32 in 79% | 17/32 in 79% | 17/32 in 79% | 17/32 in 79% | 14.05 mm 61%, over 2B | 17/32 in 79% 35/64 in 66%, over 2B | 17/32 in 79% | 13.5 mm 79% | 1 of 8 |
| 3/4-10 | 21/32 in 72% | 21/32 in 72% | 21/32 in 72% | 21/32 in 72% | 21/32 in 72% | 17.0 mm 62%, over 2B | 41/64 in 84%, under 2B 21/32 in 72% | 21/32 in 72% | 16.5 mm 77% | 2 of 8 |
| 7/8-9 | 49/64 in 76% | 49/64 in 76% | 49/64 in 76% | 49/64 in 76% | not listed | 20.0 mm 61%, over 2B | 49/64 in 76% 25/32 in 65%, over 2B | 49/64 in 76% | 19.5 mm 74% | 2 of 7 |
| 1/4-28 | #3 80% | #3 80% | #3 80% | #3 80% | #3 80% 7/32 in 67% | 5.5 mm 72% | #3 80% 5.5 mm 72% | 5.5 mm 72% | 5.5 mm 72% | 3 of 8 |
| 5/16-24 | letter I 75% | letter I 75% | letter I 75% | letter I 75% | letter I 75% | 6.9 mm 75% | 6.8 mm 83% letter I 75% | 6.9 mm 75% | 6.9 mm 75% | 0 of 8 |
| 3/8-24 | letter Q 79% | letter Q 79% | letter Q 79% | letter Q 79% | letter Q 79% 21/64 in 87%, under 2B | 8.5 mm 75% | letter Q 79% 8.5 mm 75% | 8.5 mm 75% | 8.5 mm 75% | 3 of 8 |
| 7/16-20 | 25/64 in 72% | 25/64 in 72% | 25/64 in 72% | 25/64 in 72% | 25/64 in 72% | 9.9 mm 73% | letter W 79% 25/64 in 72% | 9.9 mm 73% | 9.9 mm 73% | 3 of 8 |
| 1/2-20 | 29/64 in 72% | 29/64 in 72% | 29/64 in 72% | 29/64 in 72% | 29/64 in 72% | 11.5 mm 73% | 11.4 mm 79% 29/64 in 72% | 11.5 mm 73% | 11.5 mm 73% | 0 of 8 |
| 9/16-18 | 33/64 in 65% | 33/64 in 65%, over 2B | 33/64 in 65%, over 2B | 33/64 in 65%, over 2B | 33/64 in 65%, over 2B | 12.9 mm 76% | 1/2 in 87%, under 2B 33/64 in 65%, over 2B | 13.0 mm 70% | 12.9 mm 76% | 3 of 8 |
| 5/8-18 | 37/64 in 65% | 37/64 in 65%, over 2B | 37/64 in 65%, over 2B | 37/64 in 65%, over 2B | 37/64 in 65%, over 2B | 14.5 mm 75% | 9/16 in 87%, under 2B 37/64 in 65%, over 2B | 14.5 mm 75% | 14.5 mm 75% | 3 of 8 |
| 3/4-16 | 11/16 in 77% | 11/16 in 77% | 11/16 in 77% | 11/16 in 77% | 11/16 in 77% | 17.5 mm 75% | 11/16 in 77% 17.5 mm 75% | 17.5 mm 75% | 17.5 mm 75% | 3 of 8 |
| 7/8-14 | 13/16 in 67% | 13/16 in 67% | 13/16 in 67% | 13/16 in 67% | not listed | 20.4 mm 77% | 51/64 in 84%, under 2B 13/16 in 67% | 20.5 mm 73% | 20.4 mm 77% | 3 of 7 |
| 1/2-28 | 15/32 in 67% | not listed | 15/32 in 67% | not listed | not listed | not listed | not listed | 11.8 mm 76% | not listed | 1 of 2 |
| 5/8-24 | 37/64 in 87% | not listed | 37/64 in 87%, under 2B | not listed | not listed | not listed | not listed | 14.75 mm 82% | not listed | 1 of 2 |
Where a chart prints more than one drill, all are shown in its order. Drills within 0.0005 in of each other count as the same size, so 5.1 mm matches #7.
The Starrett tap drill chart
Starrett's chart (Bulletin 1317) is laid out by drill: each drill size is listed with its decimal equivalent and the tap it is used for. These are its drills for the threads on this site. The inch drills match American Fastener and Little Machine Shop wherever Starrett lists the thread. The metric column has one difference, 6.7 mm for M8 where Emuge and Hartner give 6.8 mm.
| Thread | Starrett drill | Size | Thread left | Class 2B or 6H hole |
|---|---|---|---|---|
| #0-80 | 3/64 in | 0.0469 in (1.19 mm) | 81% | Inside 2B |
| #2-56 | #50 | 0.0700 in (1.78 mm) | 69% | Inside 2B |
| #4-40 | #43 | 0.0890 in (2.26 mm) | 71% | Inside 2B |
| #5-40 | #38 | 0.1015 in (2.58 mm) | 72% | Inside 2B |
| #6-32 | #36 | 0.1065 in (2.71 mm) | 78% | Inside 2B |
| #6-40 | #33 | 0.1130 in (2.87 mm) | 77% | Inside 2B |
| #8-32 | #29 | 0.1360 in (3.45 mm) | 69% | Inside 2B |
| #10-24 | #25 | 0.1495 in (3.80 mm) | 75% | Inside 2B |
| #10-32 | #21 | 0.1590 in (4.04 mm) | 76% | Inside 2B |
| #12-24 | #16 | 0.1770 in (4.50 mm) | 72% | Inside 2B |
| 1/4-20 | #7 | 0.2010 in (5.11 mm) | 75% | Inside 2B |
| 5/16-18 | letter F | 0.2570 in (6.53 mm) | 77% | Inside 2B |
| 3/8-16 | 5/16 in | 0.3125 in (7.94 mm) | 77% | Inside 2B |
| 7/16-14 | letter U | 0.3680 in (9.35 mm) | 75% | Inside 2B |
| 1/2-13 | 27/64 in | 0.4219 in (10.72 mm) | 78% | Inside 2B |
| 9/16-12 | 31/64 in | 0.4844 in (12.30 mm) | 72% | Inside 2B |
| 5/8-11 | 17/32 in | 0.5313 in (13.49 mm) | 79% | Inside 2B |
| 3/4-10 | 21/32 in | 0.6563 in (16.67 mm) | 72% | Inside 2B |
| 7/8-9 | 49/64 in | 0.7656 in (19.45 mm) | 76% | Inside 2B |
| 1/4-28 | #3 | 0.2130 in (5.41 mm) | 80% | Inside 2B |
| 5/16-24 | letter I | 0.2720 in (6.91 mm) | 75% | Inside 2B |
| 3/8-24 | letter Q | 0.3320 in (8.43 mm) | 79% | Inside 2B |
| 7/16-20 | 25/64 in | 0.3906 in (9.92 mm) | 72% | Inside 2B |
| 1/2-20 | 29/64 in | 0.4531 in (11.51 mm) | 72% | Inside 2B |
| 9/16-18 | 33/64 in | 0.5156 in (13.10 mm) | 65% | 0.0006 in over the 2B maximum |
| 5/8-18 | 37/64 in | 0.5781 in (14.68 mm) | 65% | 0.0001 in over the 2B maximum |
| 3/4-16 | 11/16 in | 0.6875 in (17.46 mm) | 77% | Inside 2B |
| 7/8-14 | 13/16 in | 0.8125 in (20.64 mm) | 67% | Inside 2B |
| M2 | 1.6 mm | 0.0630 in | 77% | Inside 6H |
| M2.5 | 2.05 mm | 0.0807 in | 77% | Inside 6H |
| M3 | 2.5 mm | 0.0984 in | 77% | Inside 6H |
| M3.5 | 2.9 mm | 0.1142 in | 77% | Inside 6H |
| M4 | 3.3 mm | 0.1299 in | 77% | Inside 6H |
| M5 | 4.2 mm | 0.1654 in | 77% | Inside 6H |
| M6 | 5.0 mm | 0.1969 in | 77% | Inside 6H |
| M8 | 6.7 mm | 0.2638 in | 80% | Inside 6H |
| M10 | 8.5 mm | 0.3346 in | 77% | Inside 6H |
| M12 | 10.2 mm | 0.4016 in | 79% | Inside 6H |
| M14 | 12.0 mm | 0.4724 in | 77% | Inside 6H |
| M16 | 14.0 mm | 0.5512 in | 77% | Inside 6H |
| M18 | 15.5 mm | 0.6102 in | 77% | Inside 6H |
| M20 | 17.5 mm | 0.6890 in | 77% | Inside 6H |
| M22 | 19.5 mm | 0.7677 in | 77% | Inside 6H |
| M24 | 21.0 mm | 0.8268 in | 77% | Inside 6H |
| M30 | 26.5 mm | 1.0433 in | 77% | Inside 6H |
Starrett does not list 1/2-28 and 5/8-24. Its 9/16-18 and 5/8-18 drills are the standard ones, so they share the small overshoot of the 2B maximum described below.
The Little Machine Shop tap drill chart
Little Machine Shop prints two tap drill columns, one for a 75% thread in aluminum, brass and plastics and one for a 50% thread in steel, stainless and iron, plus close and free fit clearance drills. Its 75% column gives the standard drill for all 30 inch threads on this site, including the extra-fine 1/2-28 and 5/8-24. Fabworks and Microform Precision print the same values. Because it follows the standard drill, it also has the three drills outside class 2B: 33/64 in for 9/16-18, 37/64 in for 5/8-18 and 37/64 in for 5/8-24. We did not compare its 50% column.
Where the charts part ways
Emuge and Hartner: metric drills, inside the 2B limits
Emuge differs from the standard drill on 17 of 30 threads, and Hartner (Gühring group) on 22 of 27, mostly because both give metric drills. Emuge's drill is bigger than the standard on twelve threads, so it leaves less thread, and smaller on five fine threads where the standard drill leaves 72% or less. Both charts print the class 2B minor diameter limits next to each drill, and every drill they give falls inside them.
Champion lists a smaller drill first
Champion Cutting Tool gives two or three drills for 27 threads, always with the smaller drill first. Next to each drill it prints a "probable percentage of thread", and those figures run below the formula's. For #7 on 1/4-20, Champion prints 70% and the formula gives 75%. Across the chart, Champion's figure is about 5 points lower. The chart does not say how its figures are worked out. Measured by the drill's own diameter, five of the drills it lists first are under the 2B minimum: 15/32 in for 9/16-12, 41/64 in for 3/4-10, 1/2 in for 9/16-18, 9/16 in for 5/8-18 and 51/64 in for 7/8-14.
Engineering Toolbox's coarse drills run big
Engineering Toolbox gives metric drills. On #10-24, #12-24, 1/4-20, 5/16-18, 3/8-16, 7/16-14, 1/2-13, 9/16-12, 5/8-11, 3/4-10 and 7/8-9, they leave 60% to 62% thread and cut a hole over the 2B maximum. Its fine-thread drills match Hartner's on all 11 fine threads both list.
Bolt Depot gives #35 for 6-32
Bolt Depot lists the standard drill everywhere except on #6-32, where it gives #35 or 7/64 in. It also lists a fractional drill for many sizes. Four of those fall outside the 2B limits: 5/32 in for #10-24 (over), 17/64 in for 5/16-18 (over), 23/64 in for 7/16-14 (under) and 21/64 in for 3/8-24 (under).
The standard drill misses on three threads
American Fastener, Little Machine Shop and Starrett print the same standard drill, and on 9/16-18, 5/8-18 and 5/8-24 it falls outside the 2B limits. 33/64 in for 9/16-18 is over the max by 0.0006 in, 37/64 in for 5/8-18 is over the max by 0.0001 in and 37/64 in for 5/8-24 is under the min by 0.0019 in. Emuge gives 13.0 mm for 9/16-18, 14.5 mm for 5/8-18 and 14.75 mm for 5/8-24, all inside.
Which chart to use
If you have your tap maker's chart, use its drill for that tap. Without one, use the standard drill, which most charts print. If a drawing calls for class 2B, check the hole against the limits: the thread percentage chart lists them for every thread, and Emuge's and Hartner's drills stay inside.
For tough metal, a bigger drill makes the tap easier to turn. The steel and stainless columns of the tap drill chart give one, but on most inch threads it cuts a hole over the 2B maximum, so use it where the drawing names no thread class.
Metric tap drill charts compared
Metric charts mostly agree on the major diameter minus the pitch. M8 is the exception: 8 mm minus the 1.25 mm pitch is 6.75 mm, which falls between two drill sizes. Starrett and Champion Cutting Tool give 6.7 mm (80%), and the rest give 6.8 mm (74%). Both are inside the 6H limits of 6.647 to 6.912 mm.
Bolt Depot's metric page says its drills are for 75% depth of thread, but on eight of the nine sizes it lists they are 0.1 to 0.3 mm bigger than the other charts' drills. By the formula they leave 62% to 69% thread, and on M6, M10 and M12 the hole is over the 6H maximum.
| Thread | Major minus pitch | Starrett | Bolt Depot | Champion Cutting Tool | Emuge | Hartner |
|---|---|---|---|---|---|---|
| M2 | 1.6 mm 77% | 1.6 mm 77% | not listed | 1.6 mm 77% | 1.6 mm 77% | 1.6 mm 77% |
| M2.5 | 2.05 mm 77% | 2.05 mm 77% | not listed | 2.05 mm 77% | 2.05 mm 77% | 2.05 mm 77% |
| M3 | 2.5 mm 77% | 2.5 mm 77% | 2.5 mm 77% | 2.5 mm 77% | 2.5 mm 77% | 2.5 mm 77% |
| M3.5 | 2.9 mm 77% | 2.9 mm 77% | not listed | 2.9 mm 77% | 2.9 mm 77% | 2.9 mm 77% |
| M4 | 3.3 mm 77% | 3.3 mm 77% | 3.4 mm 66% | 3.3 mm 77% | 3.3 mm 77% | 3.3 mm 77% |
| M5 | 4.2 mm 77% | 4.2 mm 77% | 4.3 mm 67% | 4.2 mm 77% | 4.2 mm 77% | 4.2 mm 77% |
| M6 | 5.0 mm 77% | 5.0 mm 77% | 5.2 mm 62%, over 6H | 5.0 mm 77% | 5.0 mm 77% | 5.0 mm 77% |
| M8 | 6.8 mm 74% | 6.7 mm 80% | 6.9 mm 68% | 6.7 mm 80% | 6.8 mm 74% | 6.8 mm 74% |
| M10 | 8.5 mm 77% | 8.5 mm 77% | 8.7 mm 67%, over 6H | 8.5 mm 77% | 8.5 mm 77% | 8.5 mm 77% |
| M12 | 10.2 mm 79% | 10.2 mm 79% | 10.5 mm 66%, over 6H | 10.2 mm 79% | 10.2 mm 79% | 10.2 mm 79% |
| M14 | 12.0 mm 77% | 12.0 mm 77% | 12.2 mm 69% | 12.0 mm 77% | 12.0 mm 77% | 12.0 mm 77% |
| M16 | 14.0 mm 77% | 14.0 mm 77% | 14.2 mm 69% | 14.0 mm 77% | 14.0 mm 77% | 14.0 mm 77% |
| M18 | 15.5 mm 77% | 15.5 mm 77% | not listed | 15.5 mm 77% | 15.5 mm 77% | 15.5 mm 77% |
| M20 | 17.5 mm 77% | 17.5 mm 77% | not listed | 17.5 mm 77% | 17.5 mm 77% | 17.5 mm 77% |
| M22 | 19.5 mm 77% | 19.5 mm 77% | not listed | 19.5 mm 77% | 19.5 mm 77% | 19.5 mm 77% |
| M24 | 21.0 mm 77% | 21.0 mm 77% | not listed | 21.0 mm 77% | 21.0 mm 77% | 21.0 mm 77% |
| M30 | 26.5 mm 77% | 26.5 mm 77% | not listed | 26.5 mm 77% | 26.5 mm 77% | 26.5 mm 77% |
FAQ
Why do tap drill charts give different sizes?
They round the 75% hole to different sets of drills, and some aim for a different hole. Emuge, a tap maker, and Hartner, a drill maker, give metric drills for most fine inch threads. Champion Cutting Tool lists a smaller drill first and prints a "probable" percentage below the formula's. Engineering Toolbox's metric drills for the larger coarse threads leave 60% to 62% thread.
Is #6 or #7 right for 1/4-20?
Both cut a hole inside the class 2B limits for 1/4-20 (0.1960 to 0.2070 in). #7 is the drill most charts print and leaves about 75% thread. Emuge, a tap maker, gives #6, which leaves 71% and is easier on the tap.
Is #35 or #36 right for 6-32?
#36 is the drill most charts print, at about 78% thread. Bolt Depot gives #35 (69%) and Emuge gives #34 (67%). All three cut a hole inside the 2B limits of 0.1040 to 0.1140 in.
What does the Starrett tap drill chart give?
Starrett's chart (Bulletin 1317) prints the same inch drills as American Fastener and Little Machine Shop for every thread it lists here. Its metric column differs on one size: 6.7 mm for M8 where Emuge and Hartner print 6.8 mm.
Which tap drill chart is the most accurate?
It depends on what the hole has to meet. For a class 2B thread, Emuge and Hartner are the only charts here whose every drill falls inside the 2B limits, and both print those limits next to their drills. The standard drill that most charts print is inside the limits on all but three of the 30 inch threads.
Drills from American Fastener, Little Machine Shop, Starrett, Bolt Depot, Engineering Toolbox, Champion Cutting Tool, Emuge and Hartner (Gühring group), and Bolt Depot's metric table. Hole limits: class 2B limits from the OSG chart (the UNEF threads from the YG-1 chart) and class 6H limits from the Emuge chart. Thread percentages use the formula in the OSG tap drill chart, Vol 3 (2024). Read on 20 October 2026.