Tim Watts wrote:

Re the castor cups - do you think they'd work on slate? I can see them
(assuming they are plastic) getting ground away in pretty short order.


Run of the mill castor cups are thermosetting plastic with a disc of
nylon or (in the deluxe version Teflon) bonded to the base. They will
last forever.

I recommend you find a location for the piano and aim not to move it!
Use castor cups for everyday floor protection.

If you need to move the piano occasionally to decorate behind, buy or
improvise a temporary dolly.

If you are set on using the rubber wheels shown, then screw them in
place of the existing castors.