Hot Racing Arrma Grom Steel Differential Outdrive Set. This is an optional set of outdrives intended as an upgrade for the Arrma Grom 1/18 Granite Monster Truck and Typhon Buggy platforms. CNC machined from tough steel, these outdrives provide superior durability compared to standard components. They have been precision-engineered to ensure a precise fit on the front or rear of your vehicle. Package includes two steel differential outdrives.