Called transfer balls in manufacturing, these 1" diameter polished steel balls ride on a bed of 1/8" ball bearings in a steel housing.
They can be used to make ideal roller stands for material. Unlike cylindrical rollers, these units do not have to be lined up with any part of the machine; they have no bias and give you far better control of your workpiece.
Load rating is 77 lb per ball. Fixing screws included.