Go to a plumbing supply store and ask for a 1/2 in. MIP x 3/8 in. FIP threaded Hex Bushing. Bring one of your Driftmasters to confirm the threads mate up and you’ll be good. They should have brass and stainless available. Brass bushings should run $3-4 each. Be sure to get ones with a hex head so you can get them out with a socket when you want to switch back over to the 1/2” stems. You’ll never get the shoulderless helicoil-looking ones out of your bases once you crank them down the first time... been there, done that on other projects.