Bicycle trailer coupler compatibility: suitable for most bicycles, including those with disc brakes and instep brand trailers. Not compatible with BREEZER style dropouts. Fits QR shafts and 12 mm solid shafts (outer diameter approximately 0.48 inch). High-quality material: made of durable iron with a solid structure for long-term outdoor use. Reliable trailer connector designed for strength and performance. Precise design: the hole connecting to the bicycle is 1/2 inch in diameter. The outer diameter of the axle connection part is 1 inch. The trailer side has a 1-inch diameter hole. A 12mm straight shaft requires adjustment. This replacement shaft features external threads. Family fun: additional trailer coupler accessory connector allows family bicycles to tow children's or pet trailers. Enables enjoyable cycling experiences for kids and pets. : offers high wear resistance and excellent durability. Color: black Material: iron Package Contents: 2 x traction heads Note: Light and display differences may cause slight variation in color between the image and actual item. Measurement allowance is +/- 1-3 cm.