This is the simplest version of the seat-post hitches and it's use necessitates removing the seat-post from the bike, adding the two sleeves to the seat-post and sliding the seat-post through the ring and tightening the seat-post clamp Its quicker if you have a quick- release seat clamp. Some tape on your seat-post will help protect it from wear, not too much as there has to be space to allow the ring to articulate going over bumps and up kerbs. The vertical articulation is taken care of by the threaded parts, and the horizontal swing by the ring on the seat-post. Enjoy the added theft protection afforded by this design. Sold as a separate unit $55 (US $43) for DIYers. Cargo bicycle trailers by Tony's Trailers