The tap drill for 6-32 UNC is #36 (0.1065 in, 2.71 mm), which gives about 78% of full thread depth. The exact 75% hole is 0.1076 in (2.73 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 |
|---|---|---|---|---|---|
| 2.6 mm | metric | 0.1024 | 2.60 | 88% | deep, hard to tap |
| #37 | number | 0.1040 | 2.64 | 84% | deep, hard to tap |
| 2.7 mm | metric | 0.1063 | 2.70 | 78% | |
| #36 | number | 0.1065 | 2.71 | 78% | chart drill |
| 7/64" | fraction | 0.1094 | 2.78 | 71% | |
| #35 | number | 0.1100 | 2.79 | 69% | |
| 2.8 mm | metric | 0.1102 | 2.80 | 68% | |
| #34 | number | 0.1110 | 2.82 | 67% | easier to tap |
| #33 | number | 0.1130 | 2.87 | 62% | easier to tap |
| 2.9 mm | metric | 0.1142 | 2.90 | 59% | easier to tap |
About the 6-32 thread
6-32 is the coarse #6 machine screw thread (0.138 in nominal). In the US it is the screw that holds switches and receptacles to their boxes and wall plates to devices, and in computers it is the screw for 3.5 in hard drives, many motherboard standoffs and power supplies (smaller drives and optical drives use M3). It also turns up in model engineering, small hinges, guitar pickguards and electronics enclosures.
Charts list #36 (0.1065 in), which gives a deep thread of nearly 78%. At this size the difference between a good and a broken tap is mostly technique. #6 taps are thin, so in steel and stainless many people step up to a #35 drill (about 69%): the thread is a little shallower, and the tap is much more likely to survive.
6-32 thread dimensions
| Dimension | Value | Also |
|---|---|---|
| Nominal diameter | 0.1380 in | 3.51 mm |
| Threads per inch | 32 | pitch 0.0312 in (0.794 mm) |
| Basic pitch diameter | 0.1177 in | 2.990 mm |
| Basic minor diameter (nut) | 0.1042 in | 2.646 mm |
| Tensile stress area | 0.0091 in² | 5.86 mm² |
| #6-40 UNF (same diameter): tap drill | #33 (0.1130 in) | 77% thread |
Clearance hole for #6
The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For #6 a normal fit is #25 (0.1495 in). Never drill the clearance part with the tap drill: the screw will not pass.
| Fit | Drill | Diameter |
|---|---|---|
| Close fit | #27 | 0.1440 in |
| Normal fit | #25 | 0.1495 in |
| Loose fit | #18 | 0.1695 in |
How deep to drill a blind 6-32 hole
| Part material | Full thread wanted | Drill depth (full diameter) | Depth to drill tip (118°) |
|---|---|---|---|
| Steel or cast iron (1 × diameter) | 0.138 in | 0.357 in (about 11/32″) | 0.389 in (about 3/8″) |
| Aluminium or brass (2 × diameter) | 0.276 in | 0.495 in (about 1/2″) | 0.527 in (about 17/32″) |
Wrench size for #6
- Machine screw hex nut: 5/16 in wrench
- Socket head cap screw: 7/64 in hex key
SAE bolt grades start at 1/4 in, so there is no graded torque for #6 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 6-32
| Thread | Diameter (in) | Diameter (mm) | Pitch |
|---|---|---|---|
| #6-32 UNC (this page) | 0.1380 | 3.51 | 32 TPI (0.79 mm) |
| #6-40 UNF | 0.1380 | 3.51 | 40 TPI (0.64 mm) |
| M3.5 x 0.6 | 0.1378 | 3.50 | 0.6 mm (42.3 TPI) |
Tips for tapping 6-32
- Do not use a drill driver to tap #6 by hand; a small T-handle tap wrench gives the feel you need to stop before the tap binds.
- In plastic enclosures, a thread-forming screw or a heat-set insert is usually better than a tapped 6-32 thread.
- Computer cases: a coarse 6-32 screw forced into an M3 standoff will cross-thread it. M3 screws have finer, closer threads and a smaller head.
- For a stripped device screw hole in a metal electrical box, re-tap with 6-32 or use the box maker’s repair clip; do not drill the box out to a larger size.
Frequently asked questions
What size drill bit for a 6-32 tap?
#36 (0.1065 in), which gives about 78% thread. The exact 75% size is 0.1076 in (2.73 mm).
How deep should a blind 6-32 hole be?
For a full thread of 1 × diameter in steel, drill about 0.357 in (about 11/32″) at full diameter with a plug tap, or 0.389 in (about 3/8″) to the drill tip; in aluminium, about 0.495 in (about 1/2″).
What is the tap drill for 6-32 in mm?
About 2.7 mm. 2.7 mm (0.106 in) is almost exactly the #36 drill.
Is 6-32 the same as M3?
No. M3 x 0.5 is 0.118 in in diameter against 0.138 in for #6, and its pitch is finer. They are close enough to cause mix-ups in a parts bin but are not interchangeable.
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.