This is the place to get your 4-wheel dollies.
Furniture dollies, also called 4-wheel dollies, are ideal for transport
over level surfaces (no stairs) of couches, pianos on piano boards,
upright pianos, and so on.
4-wheelers can be made of plastic or 1/2" wood from U-Haul on the low end
to professional 4-wheelers made of 3/4" oak and topped with gorilla grip.
4-wheel dollies can go for $20 on the low end to over $100 for
professional grade.