1/4-28 UNF tap drill size

#3 drill — 0.2130 in / 5.41 mm (80% thread)

Major Ø 0.2500 in · 28 threads per inch · fine series. The chart pick targets 75% thread; nearby standard drills:

Drill	Decimal (in)	mm	Thread %
#2	0.2210	5.61	63%
7/32	0.2188	5.56	67%
#3	0.2130	5.41	80%
#4	0.2090	5.31	88%

Cut taps only — roll-form taps need a larger hole. 65–75% suits general work; drop toward 55% in tough material. Verify before you cut.

Same size, coarse series: 1/4-20 UNC