CIPA Towing Mirror installation knobs are made with durable ABS plastic known for its strength, rigidity, and unbreakable security. The installation wedge is formed from polypropylene plastic that has excellent long-term shape conformity, and provides years of installation reliability. This kit replaces the small pieces that come with Custom Towing Mirror part numbers 11550, 11551, and 11552. It includes 2 installation knobs, 1 right hand installation wedge, 1 left hand installation wedge, and 4 felt strips.