2Pc Red Nautilus Compact Hybrid Electric/Air Horn 139Db With Relay For 12V P5 for Chevrolet Silverado 3500 HD This is for a set of two (2)horns for 12V systems with wire relay. Mounts easily to wherever you choose to place horn. Measurements 150x112x95mm (125x112x78 mm compact) Perfect for all vehicles!.