Rubber Grommets and Push-In Bumpers Heyco Rubber Grommets and Rubber Push-In Bumpers are designed for through hole protection and are constructed of SBR. Available in 160 diameters from 0.250' to 2.5', Heyco's Rubber Grommets cover sharp edges to protect wires and add aesthetic value. Heyco's Rubber Push-In Bumpers fit snugly into the opening to prevent the entry of air and liquid.