Silver Road Warrior 18" Aluminum Tire Thread Checker Thumper Knocker Bat big rig truck billy Corrosion resistant heavy-duty aluminum 'billy' bat with tapered thermal-rubber grip and a wrist-strap that doubles as a storage hanger. Silver Aluminum with Clear Coat Finish A properly inflated tire will produce a sharp "thwack" sound when hit, and the thumper will bounce back sharply.