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 (outer diameter) solid shafts, 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 diameter connecting to the bicycle is 1/2 inch; 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 bikes to tow children's or pet trailers. Enables enjoyable cycling experiences for kids or pets. : high wear resistance and excellent durability. Color: black Material: iron Package Contents: 2 x traction heads Note: Light and display differences may cause slight variations in color between the image and actual item. Measurement error allowance is +/- 1-3 cm.