Pilot Hole Sizes for Screws

Standard/Specialty Industrial machine screws and industrial fasteners, including Lo-Driv Screws and Tri-Round screws, are available in various diameters and materials. The chart below lists the Lo-Driv and Tri-Round recommended pilot hole sizes for both inch and metric screws.

Lo-Driv & Tri-Round Recommended Pilot Holes Sizes – Inch Screws

Material Thickness Inch Nominal Screw Size Diameter – TPI Inch Approx.US Gauge Material .020 – .055
26 – 17
Diameter
.061 – .122
16 – 11
Diameter
.125 – .245
11 – 3
Diameter
.250 – .312
3 – 5/16″
Diameter
.313 – .500
5/16″ – 1/2″
Diameter
4 – 40 Steel*
Aluminum**
.098
.098
.102
.100
.104
.102
6 – 32 Steel
Aluminum
.120
.120
.120
.120
.125
.125
.128
.125
8 – 32 Steel
Aluminum
.147
.147
.150
.150
.154
.152
10 – 24 Steel
Aluminum
.166
.166
.172
.166
.177
.170
10 – 32 Steel
Aluminum
.173
.173
.177
.173
.180
.177
12 – 24 Steel
Aluminum
.193
.191
.199
.196
.203
.199
1/4 – 20 Steel
Aluminum
.219
.219
.224
.221
.228
.224
.234
.228
5/16 – 18 Steel
Aluminum
.281
.278
.288
.284
.290
.286
3/8 – 16 Steel
Aluminum
.342
.339
.348
.343
.350
.343

Lo-Driv & Tri-Round Recommended Pilot Holes Sizes – Metric Screws

Material Thickness Nominal Screw Size Dia. Pitch Millimeters
Material
.05 – 1.2 Diameter 1.3 – 2.4 Diameter 2.5 – 4.0 Diameter 4.1 – 5.9 Diameter 6.0 – 8.1 Diameter
M3 x 0.5 Steel 2.72 2.74 2.77
M4 x .07 Steel 3.58 3.60 3.63 3.68
M5 x 0.8 Steel 4.55 4.57 4.60 4.65
M6 x 1.0 Steel 5.41 5.46 5.51 5.54
M7 x 1.0 Steel 6.45 6.51 6.58
M8 x 1.25 Steel 7.31 7.39 7.47
M10 x 1.50 Steel 9.10 9.17 9.27
* Steel: Low carbon sheet and bar; average Rockwell – “B”55 – 75.** Aluminum: Aluminum sheet and bar (including aluminum andzinc die castings and all alloys in Rockwell “B” hardnessrange from 40 – 70) and other ductile materials of similar hardness, such as brass, bronze, etc.Note:Special materials and applications may warrant special hole sizes. Information available upon request.