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Drill Sizes and Tap Drills

Decimal equivalents for fractional, number and letter drills, plus the tap drill for each common UNC and UNF thread. These are the standard values used on every shop drill chart.

Decimal Equivalents

All three drill series in one list, smallest to largest. Number drills run from #80 (smallest) to #1, and letter drills from A to Z pick up where #1 leaves off.

Show:
Fraction or drill sizeDecimal (in)Tap size
#80Number.0135
#79Number.0145
1/64"Fraction.0156
#78Number.0160
#77Number.0180
#76Number.0200
#75Number.0210
#74Number.0225
#73Number.0240
#72Number.0250
#71Number.0260
#70Number.0280
#69Number.0292
#68Number.0310
1/32"Fraction.0313
#67Number.0320
#66Number.0330
#65Number.0350
#64Number.0360
#63Number.0370
#62Number.0380
#61Number.0390
#60Number.0400
#59Number.0410
#58Number.0420
#57Number.0430
#56Number.0465
3/64"Fraction.0469#0-80
#55Number.0520
#54Number.0550
#53Number.0595#1-64, #1-72
1/16"Fraction.0625
#52Number.0635
#51Number.0670
#50Number.0700#2-56, #2-64
#49Number.0730
#48Number.0760
5/64"Fraction.0781
#47Number.0785#3-48
#46Number.0810
#45Number.0820#3-56
#44Number.0860
#43Number.0890#4-40
#42Number.0935#4-48
3/32"Fraction.0938
#41Number.0960
#40Number.0980
#39Number.0995
#38Number.1015#5-40
#37Number.1040#5-44
#36Number.1065#6-32
7/64"Fraction.1094
#35Number.1100
#34Number.1110
#33Number.1130#6-40
#32Number.1160
#31Number.1200
1/8"Fraction.1250
#30Number.1285
#29Number.1360#8-32, #8-36
#28Number.1405
9/64"Fraction.1406
#27Number.1440
#26Number.1470
#25Number.1495#10-24
#24Number.1520
#23Number.1540
5/32"Fraction.1563
#22Number.1570
#21Number.1590#10-32
#20Number.1610
#19Number.1660
#18Number.1695
11/64"Fraction.1719
#17Number.1730
#16Number.1770#12-24
#15Number.1800
#14Number.1820#12-28
#13Number.1850
3/16"Fraction.1875
#12Number.1890
#11Number.1910
#10Number.1935
#9Number.1960
#8Number.1990
#7Number.20101/4"-20
13/64"Fraction.2031
#6Number.2040
#5Number.2055
#4Number.2090
#3Number.21301/4"-28
7/32"Fraction.2188
#2Number.2210
#1Number.2280
ALetter.2340
15/64"Fraction.2344
BLetter.2380
CLetter.2420
DLetter.2460
1/4"Fraction.2500
ELetter.2500
FLetter.25705/16"-18
GLetter.2610
17/64"Fraction.2656
HLetter.2660
ILetter.27205/16"-24
JLetter.2770
KLetter.2810
9/32"Fraction.2813
LLetter.2900
MLetter.2950
19/64"Fraction.2969
NLetter.3020
5/16"Fraction.31253/8"-16
OLetter.3160
PLetter.3230
21/64"Fraction.3281
QLetter.33203/8"-24
RLetter.3390
11/32"Fraction.3438
SLetter.3480
TLetter.3580
23/64"Fraction.3594
ULetter.36807/16"-14
3/8"Fraction.3750
VLetter.3770
WLetter.3860
25/64"Fraction.39067/16"-20
XLetter.3970
YLetter.4040
13/32"Fraction.4063
ZLetter.4130
27/64"Fraction.42191/2"-13
7/16"Fraction.4375
29/64"Fraction.45311/2"-20
15/32"Fraction.4688
31/64"Fraction.48449/16"-12
1/2"Fraction.5000
33/64"Fraction.51569/16"-18
17/32"Fraction.53135/8"-11
35/64"Fraction.5469
9/16"Fraction.5625
37/64"Fraction.57815/8"-18
19/32"Fraction.5938
39/64"Fraction.6094
5/8"Fraction.6250
41/64"Fraction.6406
21/32"Fraction.65633/4"-10
43/64"Fraction.6719
11/16"Fraction.68753/4"-16
45/64"Fraction.7031
23/32"Fraction.7188
47/64"Fraction.7344
3/4"Fraction.7500
49/64"Fraction.76567/8"-9
25/32"Fraction.7813
51/64"Fraction.7969
13/16"Fraction.81257/8"-14
53/64"Fraction.8281
27/32"Fraction.8438
55/64"Fraction.8594
7/8"Fraction.87501"-8
57/64"Fraction.8906
29/32"Fraction.9063
59/64"Fraction.92191"-12
15/16"Fraction.9375
61/64"Fraction.9531
31/32"Fraction.9688
63/64"Fraction.9844
1"Fraction1.0000

Tap Drill Sizes (Unified Threads)

Tap drills for about 75% thread engagement, the usual shop standard. Some charts list a size one step different for a few threads. For critical work, follow the drawing or the manufacturer's data.

ThreadSeriesTap drillDecimal (in)
#0-80UNF (fine)3/64".0469
#1-64UNC (coarse)#53.0595
#1-72UNF (fine)#53.0595
#2-56UNC (coarse)#50.0700
#2-64UNF (fine)#50.0700
#3-48UNC (coarse)#47.0785
#3-56UNF (fine)#45.0820
#4-40UNC (coarse)#43.0890
#4-48UNF (fine)#42.0935
#5-40UNC (coarse)#38.1015
#5-44UNF (fine)#37.1040
#6-32UNC (coarse)#36.1065
#6-40UNF (fine)#33.1130
#8-32UNC (coarse)#29.1360
#8-36UNF (fine)#29.1360
#10-24UNC (coarse)#25.1495
#10-32UNF (fine)#21.1590
#12-24UNC (coarse)#16.1770
#12-28UNF (fine)#14.1820
1/4"-20UNC (coarse)#7.2010
1/4"-28UNF (fine)#3.2130
5/16"-18UNC (coarse)F.2570
5/16"-24UNF (fine)I.2720
3/8"-16UNC (coarse)5/16".3125
3/8"-24UNF (fine)Q.3320
7/16"-14UNC (coarse)U.3680
7/16"-20UNF (fine)25/64".3906
1/2"-13UNC (coarse)27/64".4219
1/2"-20UNF (fine)29/64".4531
9/16"-12UNC (coarse)31/64".4844
9/16"-18UNF (fine)33/64".5156
5/8"-11UNC (coarse)17/32".5313
5/8"-18UNF (fine)37/64".5781
3/4"-10UNC (coarse)21/32".6563
3/4"-16UNF (fine)11/16".6875
7/8"-9UNC (coarse)49/64".7656
7/8"-14UNF (fine)13/16".8125
1"-8UNC (coarse)7/8".8750
1"-12UNF (fine)59/64".9219

Reading a thread size

1/4"-20 means a 1/4-inch diameter with 20 threads per inch. Machine screw sizes below 1/4" use gauge numbers, so #10-32 is a #10 screw (0.190") with 32 threads per inch. UNC is the coarse series and UNF the fine series.

Not sure which kind of drill to use? See Drill Types. Rivet hole sizes for aircraft structure are on the Aviation Hardware chart.