Rethreading a stripped bolt-hole is done by using a tap and a wrench. The tap is a vertically shaped piece of metal that have threads cut into the surface of the metal. By inserting the tap into the bolt-hole and turning it in a clockwise direction, the new threads can be cut. There are two types of tap wrenches: a T-handle and a horizontal tap wrench. Both of these devices operate the same. The T-handle allows you to tap holes in tight locations due to the T-handle that can slide from side to side.
Open the jaws of the tap wrench. The horizontal wrench will have one of the handles that move the holding jaws in and out. Turn the handle in a counterclockwise direction to open the jaws and clockwise to close them. The T-handle uses a collet like a drill chuck to hold the square end of the tap. Open the collet by turning it in a counterclockwise direction and a clockwise turn will close around the tap's square neck.
Insert the tap into the wrench and tighten. The work piece that you are going to tap should be held securely to a worktable or bench surface. You can place the piece in a vice or use a clamping mechanism.
Squirt a couple of drops of the lubrication tap oil into the hole to be tapped. Hold the tap wrench so the tap itself is perpendicular to the surface of the work piece. The tap body must be aligned squarely, perfectly straight up and down, to the hole.
Turn the tap handle in a clockwise direction to start the tap into the hole. Make two full clockwise rounds or turns with the handle.
Reverse the direction of the wrench and remove the tap. Remove any metal debris from the hole. Repeat Step 4 for another two full rounds past the last point. Remove the tap and clean the hole.
Continue advancing two full rounds and removing the tap until you have reached the needed depth. You must remove the metal particles that are formed from the metal tap. If you do not, the tap could become lodged in the hole and break.
Use a tap lubricating oil for steels. Aluminium and other soft metals such as brass can be lubricated with a window cleaner such as Windex. Lubrication tap oils used on soft metals may cause the metal particles to stick in the hole. The spray action from the applicator will flush out the material from the bottom of the hole.