How to Measure a Screw
Length, diameter (gauge), and thread pitch — a step-by-step walkthrough using calipers, a thread gauge, or plain household tools.
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Technical, measurement-first guides for identifying, measuring, and specifying screws and bolts. No fluff. Just the numbers and the diagrams you need.
How to Measure a Bolt
Under-head length, major diameter, thread pitch, and grade markings — the four measurements that fully identify any bolt.
Read guideScrew Size Identifier
Pillar reference covering every common screw designation, gauge-to-millimeter conversions, and when each system is used.
Read guideBolt Size Identifier
Hex, socket cap, carriage, and flange bolts — how to read the designation and confirm it with a caliper and thread gauge.
Read guideMetric vs SAE Bolt Conversion
Side-by-side charts for M-series and fractional bolts. Which sizes are close cousins, which ones will cross-thread, and how to tell.
Read guideM6 vs 1/4-20: Are They Interchangeable?
They look identical but they're not. Exact diameter and thread pitch differences, what happens when you force them, and how to tell them apart fast.
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