Fastener Chart

Screw, bolt, and thread sizes

Fastener callouts pack a lot into a few characters, and mixing up imperial and metric threads is an easy way to strip a hole. This chart lays out common screw and bolt sizes so you can match a fastener, pick the right drill or tap, or translate between systems.

How to read a thread callout

Imperial fasteners are written as diameter–threads per inch. In "1/4-20 UNC," the 1/4 is the shaft diameter in inches and 20 is the threads per inch; UNC is coarse thread and UNF is fine. Screws smaller than 1/4" use gauge numbers instead (#4, #6, #8, and so on). Metric fasteners are written as M diameter × pitch: "M6 × 1.0" is a 6 mm shaft with 1.0 mm between threads.

Using the chart

Find your size in either system to see its matching dimensions. It's handy when a project spec is metric but your hardware store is imperial, or when you need the tap-drill size for a thread you're cutting.

Common question

Coarse or fine thread — does it matter?

Coarse threads (UNC, or a larger metric pitch) drive faster and are more forgiving in soft materials; fine threads (UNF, smaller pitch) hold better under vibration and in thin walls. They are not interchangeable — the pitch has to match the nut or tapped hole.