Bicycle trailer coupler compatible with most bicycles, including those with disc brakes and instep brand trailers. Not suitable for BREEZER style dropouts. Fits QR shafts and 12 mm solid shafts (approximately 0.48 inches in outer diameter). Made of high-quality iron with a solid structure for durable outdoor use. The hole connecting to the bicycle measures 1/2 inch in diameter, while the outer diameter of the axle connection part is 1 inch. The trailer side hole has a 1-inch diameter. A 12 mm straight shaft may require adjustment. This replacement shaft features external threads. Ideal accessory for family biking, allowing attachment of child or pet trailers. Connectors provide secure towing capability. Product is and offers high wear resistance and excellent durability. Color: black. Material: iron. Package includes: 2 x traction heads. No other items included. Note: Lighting and display differences may cause slight variations in color between image and actual item. Measurement tolerance: +/- 1-3 cm.