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 (outer diameter) solid shaft, approximately 0.48 inch. High-quality material: made of durable iron with a solid structure for long-term outdoor use. Reliable trailer connector with excellent strength and durability. Precise design: the hole connecting to the bicycle is 1/2 inch in diameter. The outer diameter of the part connecting to the axle 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 safely and comfortably. 100% and high quality: highly wear-resistant and built for lasting performance. 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.