Threads / Size reference

#12-24 UNC

#12-24 has a nominal outside diameter of 5.4864 mm and a 1.058333 mm pitch.

Nominal major diameter0.216 in

5.4864 mm

Threads per inch24 TPI

1.058333 mm pitch

Check tap-drill options →Compare #12-28 →

Nominal dimensions; no class allowances or acceptance limits applied. The # prefix denotes a numbered screw, not millimetres.

#12-24 · PITCH VIEWSCHEMATIC

same diameter comparison

#12-24 vs #12-28

#12-28 UNF shares the nominal diameter but has a 0.907143 mm pitch. The pitch difference is 0.151190 mm; these are different nominal threads.

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Nominal size comparison
Property	#12-24 UNC	#12-28 UNF
Nominal diameter · in	0.216	0.216
Nominal diameter · mm	5.4864	5.4864
Threads per inchDifferent	24	28
Pitch · mmDifferent	1.058333	0.907143

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Source chart available

Cutting-tap drill references

Cut taps · Guhring chart · PDF page 2
Target theoretical thread	Listed drill	Diameter · in / mm
55%	#13	0.185 / 4.699
65%	4.60 mm	0.181102 / 4.6
75%	4.45 mm	0.175197 / 4.45

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Need acceptance limits?

The complete class and applicable drawing requirements are needed. These nominal values are not maximum/minimum inspection limits.

Part has no marking?

Measure the correct diameter and pitch, then compare candidates across metric and inch systems.

Basis for this size

Nominal designation and family transcribed from the live directory on 2026-10-19; unit conversions are calculated using exactly 25.4 mm/in. The drill row was read from Guhring PDF page 2; numbered and letter drill diameters use page 1. Paid standard limit tables have not been reviewed.

ASME B1.1 · standard scope ↗ · Guhring · Tap Drill Sizes ↗ Full source scope →