Insert your Zirkona MaX3 knuckle or thread into the APMAMPSZM3 adapter to convert it to a 4-Hole AMPS drill-base pattern. (Mounts, holders, and devices sold separately.) This adapter measures 2 inches x 2 3/16 inches (51mm x 56mm) and also includes the Gamber Johnson NEC Triangle Hole Pattern (measures 40mm on each side) in addition to the 4-Hole AMPS pattern. The metal construction provides a sturdy connection for drilling into dashboards or other solid, flat surfaces, and is ideal for commercial or fleet use.