Repairing Fastener Threads

It often happens that we  have a fastener (bolt or nut) with damaged threads. Sometimes during installtion, the fastener threads get damaged. If the damage is not serious and  not on the load-bearing threads, then the threads can be repaired and fastener reused. Here is a fastener with partially damaged threads. Here we would only consider right-hand threads.

For thread repair, we need a tap and die set like the one shown below. Before using a die, the thread need to be lubricated with a cutting fluid. Next the thread pitch and diameter need to be measured with a thread pitch gauge and a vernier caliper (or other devices) and a die selected accordingly. Die is used for repairing external threads and tap is used for internal threads.

Insert the selected die into its holder such that markings on the die are facing upwards. Then tighten the set screw to hold the die firmly in place.

Insert the fastener in the bottom hole of the die. Turn the first few threads by hand (as if for tightening).

For ease, a gear wrench can be used to speed up the process. Turn the screw as if you are tightening it. Turns should be reversed to clear the metallic chips.

Here is the screw with repaird threads.