[joeybagadonuts]

jfong,

Maybe the ID of a 8mm pulley can be bored to 9.525mm or 3/8"

3M HTD3M 72T 18T Belt 15mm Timing Pulley Belt set kit Reduction Ratio 4:1 CNC | eBay

I agree with you, it will cost more than the inexpensive motors we shop for.
JoeyB

Thanks for the link. I haven't seen that. Although I don't think the 15 tooth pulley has enough there to bore it out to fit my 8mm shaft. Probably why I choose 20 tooth at the time.

Edit Some of my servo motors have 3/8" or larger shaft diameter. Getting a 4:1 pulley set that fits without spending $$ isn't easy. It costs more for the pulleys than the motor!!!