So, I have a gnarly tap handle and am having a helluva time finding a threaded insert to downsize the threads to fit my GS430 ****. Every fitting/insert I have found is just 2-4mm off.

The Tap Handle is 3/8"-16 and the shifter shaft is m8x1.25. Any leads or links would be much appreciated.

 

This may not be the help you're looking for, but if I were in your position, I'd just fill the tap handle with epoxy and drill/tap that. Of course, this assumes you have a tap set on hand.

 

I've considered more diy options like that but I'm confident theres a threaded insert to fit the shift thread, I've found numerous designs for the aforementioned but none in the correct size, yet that is but it would be a resort if nothing else! Thanks man!