Thread Repair Kits, Taps, Dies and Screw Extractors

Stripped hole, ruined bolt or broken screw: three repairs

Choose by what is damaged. A stripped internal thread is repaired with a helical insert kit: drill the hole oversize, cut a new thread with the supplied tap, and wind in a stainless coil that brings the hole back to its original size. A damaged bolt thread can be chased with a die. A snapped or seized screw needs an extractor. Thread locker and rivet nut tools cover related jobs: retention, and adding threads to thin sheet metal.

Thread size, pitch and standard must match exactly

A kit is only useful if its thread matches the hole. Inch threads are designated by diameter and threads per inch, such as 3/8-16 coarse or 1/2-13; metric ones by diameter and pitch, such as M8 x 1.25. Taper pipe threads like 1/8-27 NPT are different again and cannot be swapped with straight threads. Measure with a thread gauge, then check the kit's tap and drill sizes. Taps and dies in HSS cut most metals; use cutting oil.

Questions about Thread Repair Kits, Taps, Dies and Screw Extractors

What is the difference between UNC and UNF threads?

Both are inch threads. UNC is coarse, with fewer threads per inch, while UNF is fine, with more; a 1/2-13 bolt is coarse and a 1/2-20 is fine. They are not interchangeable, so measure the pitch with a gauge before choosing a kit or tap.

Which thread locker should I use, blue or red?

Blue is medium strength and lets you undo the fastener with hand tools; red is high strength and usually needs heat to release. Use blue for bolts you may service again and red only for permanent assemblies. Clean and degrease the threads before applying.

Will a screw extractor remove a snapped bolt?

Often, if you drill a centered pilot hole and turn the extractor slowly counterclockwise. Extractors are hard and brittle and can snap, which makes the job worse. Penetrating oil, heat and patience help, and a very hard or seized bolt may need drilling out instead.