This large Bell-shaped Headrest Base is made of heavy duty 11 ga steel. It is 4" tall and includes a centrally welded 7/8" receiver for standard mounting hardware. It also includes off-set mounting holes to allow optional receivers to be added to the headpad to enable it to be off-set from a mid-line mounting position. The holes can also be used, in combination with our ball & socket collars, to add lateral facial pads to the headpad.