SUGGESTED HOLE SIZES FOR TAPPING SCREWS
TYPE 1 (or D). F. G and 23 (or T)


NOMINAL DIAMETER & THREADS
HOLE
CLOSEST DRILLTO MEAN HOLE
Drill Size
Drill Diameter
Max
Mean
Min
2 - 56 0.078 0.076 0.074 48 0.0760
2 - 64 -- 0.077 -- -- --
3 - 48 0.090 0.087 0.084 44 0.0860
3 - 56 -- 0.089 -- -- --
4 - 40 0.100 0.097 0.094 41 0.0960
4 - 48 -- 0.100 -- -- --
5 - 40 0.011 0.110 0.107 35 0.1100
5 - 44 -- 0.112 -- -- --
6 - 32 0.123 0.119 0.115 31 0.1200
6 - 40 -- 0.124 -- -- --
8 - 32 0.150 0.460 0.141 20 0.1470
8 - 36 -- 0.148 -- -- --
10 - 24 0.170 0.165 0.160 19 0.1660
10 - 32 0.177 0.172 0.167 11/64 0.1719
12 - 24 0.198 0.192 0.186 11 0.1910
12 - 28 -- 0.196 -- -- --
1/4 - 20 0.228 0.221 0.214 2 0.2210
1/4 - 28 -- 0.230 -- -- --
5/16 - 18 0.289 0.281 0.273 K 0.2810
5/16 - 24 -- 0.290 -- -- --
3/8 - 16 0.349 0.339 0.329 R 0.3390
3/8 - 24 -- 0.353 -- -- --
7/16 - 14 0.409 0.397 0.385 X 0.3970
7/16 - 20 -- 0.411 -- -- --
1/2 - 13 0.471 0.457 0.443 29/64 0.4531
1/2 - 20 -- 0.475 -- -- --
FORMULA:  MEAN HOLE DIAMETER = 1.015 x basic threadpitch diameter.  Tolerance is ± 3% of mean hole diameter.  Notolerances or drill sizes are given for tapping screws with finethreads except for #10 size.  Fine thread tapping screws arenot recommended.


SUGGESTED HOLE SIZES FOR TAPPING SCREWS

TYPE AB, B, BP, BF, AND 25 (or BT)

NOMINALDIAMETER& THREADS
HOLE
CLOSEST DRILLTO MEAN HOLE
Drill Size
Drill Diameter
Max
Mean
Min
0 - 48 0.049 0.460 0.043 56 0.0465
1 - 42 0.063 0.590 0.055 53 0.0595
2 - 32 0.077 0.720 0.067 49 0.0730
3 - 28 0.090 0.840 0.078 45 0.0820
4 - 24 0.103 0.960 0.089 41 0.0960
5 - 20 0.114 0.107 0.100 36 0.1065
6 - 20 0.124 0.116 0.108 32 0.1160
7 - 19 0.138 0.129 0.120 30 0.1285
8 - 18 0.148 0.138 0.128 29 0.1360
10 - 16 0.170 0.159 0.148 21 0.1590
12 - 14 0.194 0.182 0.169 14 0.1820
1/4 - 14 0.226 0.211 0.196 4 0.2090
5/16 - 12 0.289 0.270 0.251 I 0.2720
3/8 - 12 0.356 0.333 0.310 Q 0.3320
7/16 - 10 0.413 0.386 0.359 W 0.3860
1/2 - 10 0.480 0.449 0.418 29/64 0.4531
FORMULA: MEAN HOLE DIAMETER = 0.98 x mean of threadmajor and minor diameters.  Tolerance is ± 7% of meanhole diameter
LENGTH TOLERANCES ON TYPES A, AB, BP
Nominal Screw Length
Tolerance on Length
Up to 1", incl
± 0.03
Over 1"
± 0.05
 
LENGTH TOLERANCES ON TYPES B, BF, 25, 1, F, G & 23
Nominal Screw Length
Tolerance on Length
Up to 3/4", incl
-0.03
Over 3/4" TO 1-1/2" incl
-0.05
Over 1 1/2"
-0.06

 

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