344pc SAE & Metric Thread Repair Insert Kit M5-M12, 1/4-1/2

Pull a transmission apart often enough and you will find a stripped hole. Case bolt holes in aluminum bellhousings, pan rail threads that someone ran a bolt into crooked, cooler line fitting bosses, extension housing bolts, valve body and pump bolt holes - aluminum gives up long before the steel bolt does. This 344-piece kit puts the hole back to a factory-size thread instead of sending the case to a machine shop or drilling and tapping it oversize.

It covers ten thread sizes: SAE 1/4 in, 5/16 in, 3/8 in, 7/16 in, and 1/2 in, plus metric M5, M6, M8, M10, and M12. Each size gets its own 135-degree HSS drill bit, the matching STI tap, a stack of coiled stainless wire inserts, an installation mandrel, and a tang break-off punch. Manufacturer part number MPNTRKK262-S1. Everything ships in two blow-molded cases so the sizes stay separated on the shelf.

Bench procedure is the same for every size. Drill the damaged hole out with the supplied bit, run the STI tap through it - the oversize tap is what makes room for the insert wall - blow the chips out, thread the insert on the installation tool and wind it in until the top coil sits about a half turn below the surface, then snap the drive tang off with the break-off punch. The finished hole takes the original bolt at the original torque, and because the insert is stainless the repaired hole is usually stronger than the aluminum it replaced.

The 135-degree split-point bits are the detail worth noting: they start on their own without walking, which matters when you are drilling a hole in a case you cannot chuck up in a drill press and have to do freehand with the case on the bench.