How to measure a screw before buying a replacement

Measure length from the right starting point

For a typical flat countersunk head, measure from the top of the head to the tip. For an ordinary pan or hex head, measure from the underside of the head to the tip. Unusual head shapes can use a different convention, so bring the original or its product specification if unsure.

Measure diameter across the threads

The nominal diameter relates to the outside of the threaded section, not the driver recess or the width of the head. Use calipers where available and record the units. Small differences matter: a near match between an inch size and a metric size is not evidence that they interchange.

Record the thread and head details

A matching diameter and length are not enough for a threaded hole. Metric thread pitch describes the distance between threads; inch threads are commonly identified by threads per inch. Note the head shape, driver type and any grade marking as well. Do not force an uncertain fastener into a hole.

Bring a useful sample to the store

Take the removed screw, the equipment model or a clear specification, plus the measurements. Tell staff what it fastens into and whether it is a replacement for an existing part. For a safety-critical assembly, follow the manufacturer’s specified fastener rather than substituting one that merely appears to fit.

Find a nearby location in our hardware stores directory, or continue with screw vs bolt: how to identify a useful replacement.

Published 2026-11-03 · reviewed with each rebuild, last November 2026.