Theoretical thread dimensions
Single-start 60° profile. Approximate basic values without tolerance-class allowances; these are not acceptance limits or tap-drill diameters.
- Basic pitch diameter
- 4.3104 mm
- Approx. external minor Ø
- 3.8522 mm
- Triangle height H
- 0.6874 mm
01Recognising #10-32
Check the outside diameter and use a 32 TPI pitch gauge. M5 × 0.8 is close in size, but its pitch and diameter are different. A screw starting to engage does not establish interchangeability.
02Drill and hole depth
Allied Machine lists a #21 drill, 0.159 inches. The exact conversion is 4.0386 mm; substituting a 4 mm drill changes thread engagement. In a blind hole, reserve room for the tap chamfer and chips.
03Family background and inspection
UNF belongs to the unified inch thread system. #10 is a numbered screw size, whereas 32 describes the number of threads per inch. Accept the part against the drawing’s tolerance class with suitable gauges; outside diameter alone does not establish thread fit.
Similar threads: check diameter and pitch
The UNC or UNF variant with the same diameter changes pitch. A nearby metric thread also changes diameter: check both measurements before replacing a thread.
| Thread | Ø mm | Pitch |
|---|---|---|
| #10-32 UNF | 4.826 | 32 TPI · 0.7937 mm |
| #10-24 UNC | 4.826 | 24 TPI · 1.0583 mm |
| M5 × 0.8 | 5 | 0.8 mm |
Frequently asked questions · #10-32 UNF
Is #10-32 the same as M5?
No. #10-32 has a 4.826 mm nominal diameter and 0.79375 mm pitch; M5 × 0.8 uses 5 mm and 0.8 mm.
Which tap drill is used for #10-32 UNF?
The cutting-tap reference lists #21: 0.159 inches, exactly 4.0386 mm.
Can I use a #10-24 tap?
No. #10-24 is the coarser UNC version. Use a tap marked #10-32.
Sources and standard reference
Cutting-tap drill:
Allied Machine · Unified National tap drillsASME B1.1 · Unified inch threads
Nominal reference data. The drawing, tolerance class and tool instructions govern hole preparation and acceptance. Do not automatically use a cutting-tap drill size for form tapping.
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