Pop in' type sockets mount to the bottom of amp with four super heavy duty screws. Exactly like the Fender Swivel Casters the Ernie Ball Casters are manufactured by ELCOM but the E.B. packaged version includes much larger and sturdier mounting screws. You'll have to bore a hole larger than .563" in the bottom of your amp to accommodate the long 'nose' of the 'pop in' socket. Sturdy soft rubber wheels, ball bearing swivel action. Includes sixteen mounting screws. SAVE YOUR BACK. UPC 749699161028.