I made a mobile base for my 500 pound bandsaw to raise it up a bit. The casters are non-locking, but I have lever operated feet to stabilize it.
Very rigid.
I also have some Zambus roller/feet. These are for high loads and if you have a cart, you have a pair on one end and lift/tilt the cart like a wheel barrow. That puts the wheels on the ground for rolling and when you set it back down, the adjustable feet contact the floor and act as feet, keeping the wheels up and the cart solidly in place.
