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 shaft and 12 mm solid shaft (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 construction. 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 hole is 1 inch in diameter. 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 trailers. Ideal for transporting children or pets during cycling activities. and high quality: offers high wear resistance and excellent durability. Color: black Material: iron Package Contents: 2 x traction heads Note: Only the items listed above are included. Light reflection and display differences may cause slight color variation between the image and the actual item. Measurement may vary by +/- 1-3 cm.