4" Bow Stop Polymer for 1/2 Boat Trailer Shaft Resilient, non-marring, molded Poly Vinyl bow stop. Polymer Bow Stop acts as a bumper to keep your boat from hitting your trailer winch when loading. Y-shape contours to hull to help cradle boat during trailering. Unaffected by oil, gas or salt. With proper care, should last the lifetime of your trailer! 4", 1/2" shaft.