TOO37/64 DRILL, TOO3/8NPT 3/8 Pipe tap. Not necessary, but recommended is our TOO3/8REAM 3/8 reamer as this is used after the 37/64 drill is used. The reamer is tapered which makes the tap cut the threads easier. Also, you will need to clearance the case to clear the fitting's rotation. This can be done with either a porting (Dremel) tool or a spot facer with a 37/64 pilot.
Note: it is possible to drill and tap the case together without getting any shavings in the case. To receive our exclusive copyrighted instruction at the time you buy a full flow kit from us request part number "INSD/T" and we will provide it for free. If you are not buying a complete full flow kit from us you will find this instruction in GB 800 Book of Instructions.