How to Match Nuts and Bolts by Thread Size
A nut and bolt must share the same diameter and thread pitch to thread together. A 1/4-20 bolt requires a 1/4-20 nut. If either number does not match, they will not fit.
Imperial (Inch) Fasteners
Thread size is written as diameter-TPI (threads per inch). For example, 3/8-16 means 3/8-inch diameter with 16 threads per inch. The matching nut must also be labeled 3/8-16.
Metric Fasteners
Metric thread size is written as M[diameter] x [pitch in mm]. For example, M8 x 1.25 means 8 mm diameter with a 1.25 mm thread pitch. Match the nut to both the M-size and the pitch.
Do Not Mix Imperial and Metric
Imperial and metric threads are not interchangeable. A 1/4-20 bolt looks similar in size to an M6 bolt, but the threads are different. Always confirm the measurement system before ordering.
Nut Types
- Hex nut: standard choice for most assemblies.
- Nylon lock nut: resists loosening under vibration.
- Flange nut: built-in washer face for load distribution.
Matching Tips
- Check the bolt label for diameter and TPI (or metric pitch).
- Select a nut with the exact same designation.
- Use the same material (stainless with stainless) to prevent galvanic corrosion.
- Add a washer for better load distribution.