Fastener & Mechanical Engineering
Bolt Thread Sizes & Pitch Chart
Find the exact thread pitch and tap drill size for M3 through M10 bolts. Decode tensile strength markings (8.8, 10.9) stamped on bolt heads.
Select Metric Bolt Size:
Fastener Engineering Spec
M6 × 1 Coarse Thread
Tap Drill: 5 mm
US Imperial Near-Equivalent:
1/4"-20 UNC (Camera Tripod Thread)
Fine Pitch:0.75 mm
Common Grade Markings:
Class 8.8 / 10.9
Standard Industry Uses:
Automotive engine bay brackets, motorcycle fairings, office desk assemblies.
What Do Numbers (8.8, 10.9) and Radial Lines Stamped on Bolt Heads Mean?
Class 8.8 (Metric)
800 MPa tensile strength. The standard high-tensile structural automotive bolt.
Class 10.9 (Metric)
1040 MPa tensile strength. High-stress cylinder heads, suspension links, and brake calipers.
Class 12.9 (Metric)
1220 MPa ultra-high strength. Racing engine rods and heavy industrial tooling.
Grade 5 (Imperial / 3 Radial Lines on Head)
120,000 PSI tensile strength. General automotive and trailer hitch standard.
Grade 8 (Imperial / 6 Radial Lines on Head)
150,000 PSI high tensile. Heavy truck frames, tractor implements, suspension.