| Damaged bolt hole threads can be replaced with thread repair inserts
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| Standard thread repair insert (left), and spark plug thread insert
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| Drill out the damaged threads with the specified size bit. Be sure to drill completely through the hole or to the bottom of a blind hole
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| Using the kit, tap the hole in order to receive the thread insert. Keep the tap well oiled and back it out frequently to avoid clogging the threads.
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| Screw the insert onto the installer tool until the tang engages the slot. Thread the insert into the hole until it is 1/4 - 1/2 turn below the top surface, then remove the tool and break off the tang using a punch.
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Two types of thread repair inserts are usually supplied: a standard type for most -SAE coarse, SAE fine, metric course and metric fine thread sizes and a spark plug type to fit most spark plug port sizes. Typical thread repair kits will contain a selection of pre-wound threaded inserts, a tap that corresponds to the outside diameter threads of the insert, and an installation tool. Spark plug inserts usually differ from conventional fastener inserts because they require a tap equipped with pilot threads and a combined reamer/tap section.
