EFI provides extensive fastener engineering, offshore purchasing and quality capabilities. EFI is staffed by sales engineers and import professionals with considerable background in industrial fasteners. Leading manufacturer of cold headed fasteners, tight tolerances and multiple secondary operations for precision components used in heavy-duty diesel engines, transmissions and other demanding fastener applications. Domestic quality manufacturing of small diameter fasteners and machine screws (diameters from 4-40 to 1/2" and lengths to 5"). Includes Lo-Driv® and Grip-Lite™ screws and other standard, semi-standard and specialty fastener solutions. Manufacturer of small diameter, long length fasteners. Specializing in long length, small diameter headed and threaded fasteners through 52" long and 1/2" diameter. Superior straightness in plated parts. Leader of cold-formed fasteners (diameters from 1/4" to 5/8" and lengths to 3") and industry standard and semi-standard fasteners. Efficient manufacturing processes for medium to high-volumes and provides in-house tooling. Specializes in electro deposited zinc and zinc phosphate coatings for fastener manufacturing, stamping, fabrication and metal forming industries.
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Pilot Hole Sizes for Tri-Round Screws,
Machine Screws & Industrial Fasteners

Machine screws and industrial fasteners, including Lo-Driv® 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 and zinc die castings and all alloys in Rockwell "B" hardness range 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.

Torque Tensioning
Screw Point Types
Pilot Hole Sizes
Bolt & Screw Head Types
Weights per Thousand
Unified External Screw Threads
Rod & Bolt Diameters
Metric Conversions
Hole Sizes for Die Casting
Material Strength
Drive Tool Sizes
Hardness Conversions

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