A 3/8-inch bolt with 16 threads-per-inch bolt often requires Helicoil inserts to repair damaged threads. The abundance of 3/8-16 inch bolt thread repair stems from that particular bolt being a common fastener in vehicles, construction components and manufactured metal equipment. A correctly sized hole and matched threads are required to ensure the tension style inserts remain installed, even under pressure. Drilling a hole too large for the insert will cause it to pull from the base material and you then lose the ability to use a 3/8-16 bolt in the part.
Secure a 25/64-inch drill bit in a drill motor. Coat the end of the 25/64-inch bit with a liberal amount of cutting fluid.
Drill the damaged threads from the hole with the coated drill bit. Clear metal shavings from the drilled hole with a can of compressed air.
Install a 3/8-16 tap in the tee-handle tap wrench contained in a Helicoil insert kit. Coat the 3/8-16 tap with cutting fluid. Place the end of the tap in the 25/64-inch hole. Turn the tee-handle tap wrench clockwise to cut new threads in the drilled hole. Reverse the direction of the tap to remove it from the hole. Blow metal shavings from the hole with the can of compressed air.
Thread a 3/8-16 threaded insert on the end of the Helicoil installation tool -- both components included with the installation kit. Coat the outer threads of the insert with red threadlocking sealant.
Turn the installation tool clockwise -- with the insert sitting in the threaded hole -- to install it in the hole. Reverse the direction of the tool to remove it from the insert. Place the end of the tang removal tool -- included with the Helicoil insert kit -- inside the insert. Hit the end of the tang removal tool with a hammer to break the tang from the inside of the insert to complete the repair of the 3/8-16 threads.
