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Typical Pre-Drill Pilot Hole Sizes

Typical Pre-Drill Pilot Hole Sizes

When Rotary Broaching a part a pre-drill pilot hole is required.  The typical pilot hole should be pre-drilled 3% lager than the “across the flats” dimension of the Rotary Broach.  For example, if you are using a 1/4″ Hexagon Rotary Broach the across the flats dimension is .2525 and therefore your typical pre-drill dimension would be .260.  This may vary depending upon your application, material and final product specifications. Here is a chart to show the most common pre-drill pilot hole sizes:

Hex Broach Size Across The Flats Pre-Drill Size
.050″ .0510 .053
1/16″ .0635 .065
5/64″ .0790 .081
3/32″ .0950 .098
7/64″ .1110 .114
1/8″ .1265 .130
9/64″ .1425 .147
5/32″ .1585 .163
11/64″ .1740 .179
3/16″ .1895 .196
7/32″ .2215 .228
1/4″ .2525 .260
9/32″ .2840 .293
5/16″ .3155 .325
11/32″ .3470 .357
3/8″ .3785 .390
13/32″ .4100 .422
7/16″ .4415 .455
15/32 .4730 .488
1/4″ .5045 .520
Metric Hexagon Sizes
1.3mm .0515 .053
1.5mm .0610 .063
2.0mm .0810 .083
2.5mm .1010 .104
3.0mm .1210 .125
4.0mm .1610 .166
5.0mm .2000 .206
6.0mm .2400 .247
7.0mm .2790 .287
8.0mm .3185 .328
9.0mm .3580 .369
10.0mm .3985 .410
11.0mm .4370 .450
12.0mm .4775 .492
13.0mm .5170 .533

About Polygon Solutions

Polygon Solutions manufacturers and distributes precision made rotary broach tools to manufacturers across the globe.

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