This is a nylatron wear pad by Miller Industries. It measures 6" x 1-1/2" x 3/8". It will fit the following wreckers: Vulcan 810, Vulcan 812, Century Modular Express 300 Series, Modular Midnight Express, Modular 211, Modular 400 & 600 Series, Holmes 440SL, 600R, Vulcan Modular 804, Modular 806, Modular 807, 812 Intruder, Modular 880/890, and 896/897.
Most units require 4 of these slide pads.