BA to UNC (US) Screw Conversion Chart

For converting British small screws (BA) into equivalent US screw sizes.

BA Screw

Closest US Screw

Clearance Hole

Size

TPI OD (in) Size
OD (in)
Tap Drill
(in)
Close Fit
(in)

Free Fi
(in)

BA0 25.40 0.236 ¼-20
0.250
7
0.201
F
.2570
H
.2660
BA1 28.22 0.209
BA2 31.36 0.185 #10-24
0.190
25
0.150
9
.1960
7
.2010
BA3 34.79 0.161 #8-32
0.164
29
0.136
18
.1695
16
.1770
BA4 38.48 0.142 #6-32
0.138
36
0.107
27
.1440
25
.1495
BA5 43.05 0.126
BA6 47.92 0.110 #4-40
0.112
44
0.086
32
.1160
30
.1285
BA7 52.92 0.098
BA8 59.07 0.087 #2-56
0.086
50
0.070
43
.0890
41
.0960
BA9 65.13 0.074
BA10 72.57 0.067
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