Bicycle trailer coupler compatible with most bicycles, including those with disc brakes and instep brand trailers. Not suitable for BREEZER style dropouts. Fits QR shaft and 12 mm solid shaft (outer diameter approximately 0.48 inch). Made of high-quality iron with a solid structure for durable, long-term outdoor use. Precision-designed with a 1/2 inch hole diameter connecting to the bicycle and 1 inch outer diameter where connected to the axle. The trailer connection hole is 1 inch in 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 for shared outdoor enjoyment. 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 color variations between image and actual item. Measurement tolerance is +/- 1-3 cm.