This adapter is an alternative way of attaching a trailer to a bicycle in cases where the rear wheel axle is too long or does not protrude, making it impossible to fit the conventional hitch on the axle. The part with the spring inserts into the trailer drawbar (spring diameter 21mm), while the clamp attaches to the frame (diameter 15 to 35 mm ). Take care not to pinch the brake cable or other moving parts when fitting. Compatible with trailers STORAG Always attach the trailer's safety strap to the bike.