Fastener Resources

Digital caliper measuring the major diameter of an M3 A2 stainless socket head screw at 2.90 mm
How to Measure a Screw or Bolt: Diameter, Pitch and Length
Measure an unknown screw correctly: major diameter, metric pitch or inch TPI, length by head style, drive, material and a final fit check. Read more...
Measuring a screw's outside diameter with digital calipers
Screw Thread Pitch Chart: Metric, UNC & UNF 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 socket head screws photographed side by side to compare their thread spacing
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...