Compare common fastener sizes including screw gauges, machine screws, fractional bolts, metric fasteners, decimal inches, millimeters, and thread pitch references for construction, woodworking, and hardware projects.
#6 screw diameter:
0.138 in / 3.505 mm
#8 screw diameter:
0.164 in / 4.166 mm
#10 screw diameter:
0.190 in / 4.826 mm
1/4 in bolt diameter:
0.250 in / 6.350 mm
Fastener size conversions are useful for screws, bolts, anchors, washers, drill sizing, pilot holes, hardware replacement, machine screws, woodworking, metalwork, framing, and construction layout.
Use this converter when comparing US screw gauges, fractional inch bolts, metric fasteners, decimal inches, and millimeter diameters.
Your result shows the selected fastener size converted into decimal inches, millimeters, approximate nearest fractional inch, and thread reference information.
Fastener fit can depend on thread type, head style, material, tolerance, pilot hole size, anchor type, and manufacturer specifications. Always verify final sizing for structural, mechanical, or code-sensitive work.
A common #8 screw has a major diameter of about 0.164 inches, or about 4.166 millimeters.
A common #10 screw has a major diameter of about 0.190 inches, or about 4.826 millimeters.
No. M6 is 6 mm in diameter, while 1/4 inch is 6.35 mm. They are close, but they are not the same size.
For screws and bolts, the listed major diameter usually refers to the outside diameter across the thread peaks.
No. This converter compares fastener diameters. Pilot hole size depends on material, screw type, thread design, and whether the hole is clearance, tap, or pilot.