UNF Bolts Part Thread Grade 5/S

What are UNF part-thread bolts?

These are high tensile steel hex bolts, Grade 5/S, with a UNF fine thread. UNF stands for Unified National Fine and has a finer pitch—more threads per inch (TPI)—than UNC at the same nominal diameter. UNF and UNC fasteners of the same diameter are not interchangeable.

The shaft is partly threaded, leaving a plain, unthreaded section beneath the head. The hex head is tightened with a suitable spanner or socket.

Where would I use them?

These bolts are relevant to repairs and restoration of vehicles, machinery and equipment that already use UNF fixings. Choose them where the original joint calls for a high tensile Grade 5/S bolt with a partly threaded shaft.

Match the original fixing or assembly specification rather than choosing by vehicle or machine alone. The thread, strength grade and bolt form all matter.

Part thread or full thread?

A part-thread bolt has a plain section beneath the head. If your assembly needs thread along the shaft, compare our UNF fully threaded hex setscrews, also high tensile Grade 5/S.

How do I choose the size and finish?

Check the diameter and TPI, then measure the bolt length from underneath the head to the tip. The head is not included in the length.

Select the finish available for your chosen size. Our fastener coating guide explains self colour and plated finishes.

Which nuts fit UNF bolts?

Use UNF nuts with the same diameter and TPI, and the strength specification required for the joint. Choose appropriately sized imperial washers where needed.

Unsure whether your fixing is UNF, UNC, BSF or Whitworth? Use our imperial thread identification guide before ordering.

All Available Sizes & Types