A bolt's thread, like the bolt itself, is subject to rust and corrosion as time passes. Once a bolt's thread has been corroded, it will be difficult to thread a bolt in to it. A thread tap can be used to clean out the corrosion. However, if only one thread is corroded, a thread tap will be an expensive repair solution since thread taps are sold in sets. Making a homemade thread tap is an alternative solution when a thread tap is not at hand.
Secure the bolt on a bench vice with the bolt's threaded part facing upwards. The bolt must be the same size and thread as the bolt thread, or nut, to be cleaned.
Cut a straight groove along the threaded part of the bolt using the grinder with the cutting wheel. The groove must start from the tip of the bolt's thread. The groove should only be a few millimetres deep and should be 3/4 of the bolt's length. Wear the safety goggles at all times when cutting the groove on the bolt.
Let the bolt cool down.
Release the bolt from the bench vice and turn the bolt a quarter turn to the right.
Repeat steps 2 and 3 until four groove lines have been cut in the bolt.
Screw the homemade tap bolt into the nut you need cleaned and the grooves in the bolt will push rust and debris out of the threads.
Wear safety goggles to protect your eyes.