348-Piece Thread Repair Kit Metric and SAE Helicoil

Aluminum transmission cases strip. Pan bolt holes in a 4L60E, bellhousing bolt holes on a 5R110W, the drain plug in an AW55-50SN case, a cooler line fitting boss that pulled out when somebody leaned on a wrench. Once the aluminum is gone you either weld and re-drill the case or you put a steel insert in it. This kit is the steel insert route, and it covers the sizes that actually show up on a transmission bench.

You get both thread systems in one case: metric M5, M6, M8, M10 and M12, and SAE 1/4", 5/16", 3/8", 7/16" and 1/2". Each size has its own 135-degree split-point HSS drill bit, matching STI tap, a stack of 304 stainless wire coil inserts, an installation mandrel and a tang break-off punch. 348 pieces total in a molded case so the M8 taps do not end up in the bottom of a drawer.

Working procedure is the same every time: drill the damaged hole out with the bit supplied for that size, tap it with the STI tap (go slow and back the tap out to clear chips - aluminum loads a tap fast), thread the coil insert on the mandrel and wind it in until it sits one quarter to one half turn below the surface, then snap the drive tang off with the punch. The finished hole takes a standard bolt of the original size and the stainless coil holds torque better than the parent aluminum did.

The 135-degree split point matters on a case that is already on the bench - it starts on center without a punch mark and does not walk into the sealing surface. Heat-treated alloy steel taps and tools throughout. HORUSDY part number 86591.