1/4" To 3/8" Socket Adapter
Scale to the 1/4" side being a precise fit.
The 3/8 side has tabs that can be sanded down to make that a precise fit.
The exact dimension of the 1/4" side is .254 " This worked for my well calibrated printer. So I left it as is. The 3/8" (.375") is exactly .373" not including the tabs. This left it undersized on the flat part, and over-sized on the tabs. Some light sanding on the tabs gave a perfect fit.
PLA Shatters when stressed, Print in ABS or I highly recommend PETG.
Sand the tabs on 3/8" side to fit.