The base has 1 bolt hole on base for rigid mounting when used for supporting machinery A nitrile friction pad on the base provides a non-skid surface. The ductile cast iron housing provides impact and fatigue resistance. The mount secures a heavy duty steel spring for absorbing shock and supporting the load, with nitrile sponge inserts to limit movement and prevent contact between upper and lower castings of the mount. The 110Lb payload of each hanger gives you space for heavy devices such as high end projector Can be preloaded to save valuable installation time Supplied with coupling nut Field interchangeable springs