Question 1

Can I substitute a metric fastener for an imperial one?

Accepted Answer

Not recommended. The 0.3–0.7 mm diameter differences create insufficient thread engagement or interference, which can cause joint failure. Substituting M10 for 3/8-16 may strip threads under load. Always machine parts to the specified thread system.

Question 2

How do I convert thread class (6H vs. 2B)?

Accepted Answer

ISO 6H metric tolerance approximates to UN 2B class for medium-fit applications. 4H6H (metric) ≈ 3B (UN) for precision fits, and 7H (metric) ≈ 1B (UN) for loose fits. These are approximations — for critical joints, use the standard specified by the design authority.

Question 3

Are metric and imperial drills compatible for threading?

Accepted Answer

Metric tap drills (e.g., 8.5 mm for M10×1.5) don't have exact imperial equivalents. Use the closest available drill size if needed, but preferred practice is to use the specified tap drill for the thread system being cut. For example, use a 'Q' drill (0.332 inch) for 3/8-16 UNC, not an 8.3 mm metric drill.
⚡ Calculated for Carbide-Tooling.com High-Performance Series. View Catalog →

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