Square threaded inserts to convert the end of your 1” square tubing with a nice finish for either adding wheels/casters or threaded levelers.
One set is 1/4 20 threaded white plastic inserts (caster foot) with leveling feet included. They could be replaced with wheels of the same thread size. Asking $4.50 for the set
The other set is metal and for 1 inch tubing. Has a 3/8” thread. 2 pieces Per set, 3 sets are available. Asking $4.50 each set