The tap drill for 10-24 UNC is #25 (0.1495 in, 3.80 mm), which gives about 75% of full thread depth. The exact 75% hole is 0.1494 in (3.79 mm). The table lists every number, letter, fractional and metric drill that gives between 55% and 90% thread, so you can work from the bits you own.
| Drill | Type | in | mm | Thread | Note |
|---|---|---|---|---|---|
| 3.6 mm | metric | 0.1417 | 3.60 | 89% | deep, hard to tap |
| #27 | number | 0.1440 | 3.66 | 85% | deep, hard to tap |
| 3.7 mm | metric | 0.1457 | 3.70 | 82% | deep, hard to tap |
| #26 | number | 0.1470 | 3.73 | 79% | |
| #25 | number | 0.1495 | 3.80 | 75% | chart drill |
| 3.8 mm | metric | 0.1496 | 3.80 | 75% | |
| #24 | number | 0.1520 | 3.86 | 70% | |
| 3.9 mm | metric | 0.1535 | 3.90 | 67% | easier to tap |
| #23 | number | 0.1540 | 3.91 | 67% | easier to tap |
| 5/32" | fraction | 0.1562 | 3.97 | 62% | easier to tap |
| 4 mm | metric | 0.1575 | 4.00 | 60% | easier to tap |
About the 10-24 thread
10-24 is the coarse #10 machine screw thread (0.190 in nominal). It is the #10 screw sold loose in most hardware-store drawers and used for hinges, brackets, sheet-metal enclosures, signs and cabinet hardware. Its fine sibling 10-32 looks almost the same, and mixing the two is the most common reason a #10 screw will not go in.
#25 is the usual chart drill, and it is close to the 75% target. Because #10 is near the size where metric and inch threads cross over (M5 is 0.197 in), it pays to check the pitch with a gauge or a known nut before tapping a part that already has a few threads in it.
10-24 thread dimensions
| Dimension | Value | Also |
|---|---|---|
| Nominal diameter | 0.1900 in | 4.83 mm |
| Threads per inch | 24 | pitch 0.0417 in (1.058 mm) |
| Basic pitch diameter | 0.1629 in | 4.139 mm |
| Basic minor diameter (nut) | 0.1449 in | 3.680 mm |
| Tensile stress area | 0.0175 in² | 11.31 mm² |
| #10-32 UNF (same diameter): tap drill | #21 (0.1590 in) | 76% thread |
Clearance hole for #10
The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For #10 a normal fit is #5 (0.2055 in). Never drill the clearance part with the tap drill: the screw will not pass.
| Fit | Drill | Diameter |
|---|---|---|
| Close fit | #9 | 0.1960 in |
| Normal fit | #5 | 0.2055 in |
| Loose fit | #2 | 0.2210 in |
How deep to drill a blind 10-24 hole
| Part material | Full thread wanted | Drill depth (full diameter) | Depth to drill tip (118°) |
|---|---|---|---|
| Steel or cast iron (1 × diameter) | 0.190 in | 0.482 in (about 15/32″) | 0.527 in (about 17/32″) |
| Aluminium or brass (2 × diameter) | 0.380 in | 0.672 in (about 21/32″) | 0.717 in (about 23/32″) |
Wrench size for #10
- Machine screw hex nut: 3/8 in wrench
- Socket head cap screw: 5/32 in hex key
SAE bolt grades start at 1/4 in, so there is no graded torque for #10 machine screws; tighten to the maker’s figure or until snug. Over-tightening is the usual way small tapped threads strip.
Threads easily mistaken for 10-24
| Thread | Diameter (in) | Diameter (mm) | Pitch |
|---|---|---|---|
| #10-24 UNC (this page) | 0.1900 | 4.83 | 24 TPI (1.06 mm) |
| #10-32 UNF | 0.1900 | 4.83 | 32 TPI (0.79 mm) |
| M5 x 0.8 | 0.1969 | 5.00 | 0.8 mm (31.7 TPI) |
Tips for tapping 10-24
- 10-24 has 24 threads per inch, about 1.06 mm pitch; 10-32 is about 0.79 mm, M5 is 0.8 mm. A 10-32 screw will not enter a 10-24 hole beyond a turn.
- In thin sheet metal (under about 1/8 in), there may be only two or three threads to engage. A rivet nut, a clinch nut or a plain nut gives more grip.
- A #25 drill is not in fractional sets; 5/32 in (0.156 in) is the nearest fraction and gives a shallower thread that still holds in soft metals.
- Tap small threads slowly by hand: a #10 tap is easily snapped by a drill driver.
Frequently asked questions
What size drill bit for a 10-24 tap?
#25 (0.1495 in), which gives about 75% thread. The exact 75% size is 0.1494 in (3.79 mm).
How deep should a blind 10-24 hole be?
For a full thread of 1 × diameter in steel, drill about 0.482 in (about 15/32″) at full diameter with a plug tap, or 0.527 in (about 17/32″) to the drill tip; in aluminium, about 0.672 in (about 21/32″).
Is 10-24 coarse or fine?
Coarse. 10-24 is the UNC (coarse) #10 thread; 10-32 is the UNF (fine) one.
What is the tap drill for 10-24 in mm?
About 3.8 mm or 3.9 mm. 3.8 mm is closest to the #25 drill (3.80 mm).
Sources and method
Every dimension and percentage on this page is computed from the formulas listed, not copied from another chart. Values are basic (nominal); real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric).
- ASME B1.1 and FED-STD-H28/2B (Unified inch), ISO 68-1 and ISO 261 (metric): basic thread profile and stress area formulas.
- Machinery’s Handbook (Industrial Press): percentage-of-thread relation used by our tap drill size calculator.
- ASME B94.11M twist drill series (number, letter, fractional); 0.1 mm metric drill steps.
- ISO 273 metric clearance holes; inch close, normal and loose fits as published in the ASME B18.2.8 clearance classes.
- SAE J429 and ISO 898-1 proof strengths; T = K × D × F torque relation (see our bolt torque chart for the full method).
- Wrench and hex key sizes: ASME B18.2.1, ASME B18.3, ASME B18.6.3, ISO 4014/4017, DIN 933 and ISO 4762 values as widely published.
More thread and fastener tools
- All thread and fastener charts
- UNC and UNF thread chart
- Metric thread pitch chart
- Tap drill chart (inch and metric)
- Clearance hole chart
- Nail size chart
- Wood screw size chart
- Lag screw pilot hole chart
- Bolt torque chart
- Wrench size chart
- Drill bit size chart
- Thread engagement chart
- Nail gun nail sizes by gauge
- Screw and nail size calculator
- Tap drill size calculator
- Clearance hole size calculator
- Tapped hole depth calculator
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.