|Here's what Ollie says:
A simple answer is to use a soft wheel on a hard floor and a hard wheel on carpet. Carpet is probably the only type of floor that a NYLON TWIN WHEEL caster or other Hard Wheel caster should be used on. If you have NYLON wheels on your casters, ONLY USE THEM ON CARPET - NEVER ON TILE OR WOOD as they will SLIDE AND SCRATCH THE FLOOR.
How do I tell if it's NYLON or a softer POLYURETHANE or RUBBER? Simple... Try to DENT it. Get a ball point pen and try to push it into the face of the wheel. If it dents, it is soft and probably rubber or polyurethane. If it doesn't dent, it's HARD and probably NYLON. If it is, use that only on carpet.
Also note in the photos that the "Tire" seems to be made of a different material than the wheel or the body of the caster. Most Twin Wheel casters use Nylon or Metal bodies. If the side of the wheel and the face of the wheel look like they are one piece, it is a probably NYLON wheel.
So now that you ran around the house and tested your wheels, I'm sure that you need new casters with SOFT wheels. We have a few!
Dent the Wheel
Note the look of a different material for the "Tire" & the Dent.