Stand-off insulators keep vertical antennas vertical!For best results, a vertical antenna should actually be vertical otherwise you're aiming half your RF energy into the water and not enough toward the horizon. Consists of two cast stainless-steel fittings, one attaches to the flying-bridge or upper part of your boat's structure. The other attaches to an upper antenna bracket like our Model 184234. Distance off adjustable from 3-9"