Fastener Resources

Measuring a screw's outside diameter with digital calipers
Thread Pitch Chart: UNC, UNF & Metric Thread Sizes
Identify common Unified inch and ISO metric screw threads with UNC, UNF, TPI, and metric-pitch charts, plus practical measurement guidance. Read more...
M3 and #4-40 machine screws beside a thread pitch gauge and digital calipers
M3 or #4-40: why they are not interchangeable
Compare M3 × 0.5 and #4-40 UNC dimensions, learn why the threads are not interchangeable, and identify them without damaging the mating part. Read more...