The Stock Polaris RZR XP4 900 frame has a bolt together joint. This frame includes a rear sub frame and a front sub frame, with the joint being directly under the front passengers. This joint is a week point that can bend and leave the Polaris RZR XP4 900 frame totaled, as well as injuries to you or your passengers. The ABF Polaris RZR XP4 900 Frame Gusset Kit, creates a weld-in sleeve that spans the entire passenger compartment. It sandwiches the bolt-together joint and eliminates the weak point. The Frame Gusset Kit is constructed of 11ga steel for strength.