On Friday, June 28, 2019 at 7:33:35 PM UTC-4, M. L. wrote:
I have chrome shelving kit pipes with 3/8" threads that I'd like to use
for inserting casters instead of the levelers it comes with. I have some
1/4" thread casters lying around and would like to find a way to use
them with the 3/8" threading. Is there such a thing as a 3/8" to 1/4"
threaded reducer for casters? TIA.

IDK, I googled a bit and all I found were reducing bushings for pipe threads.
Never saw one for bolt threads either.