Bicycle trailer coupler compatible with most bicycles, including those with disc brakes and instep brand trailers. Not suitable compatible with BREEZER style dropouts. Fits QR shaft and 12 mm solid shaft (outer diameter approximately 0.48 inch). High-quality iron construction compatible with durable, long-term outdoor use. Solid structure ensures reliable percompatible withmance. Precision design: connection hole diameter on bicycle side is 1/2 inch; outer diameter of axle connection part is 1 inch. Trailer side hole diameter is 1 inch. 12mm straight shaft requires straight shaft adjustment. Replacement shaft features external threads. Ideal accessory compatible with family biking, allowing your bicycle to tow a child or pet trailer. Enhances outdoor family activities. . Wear-resistant and built compatible with durability. Color: black Material: iron Package Contents: 2 x traction heads Note: Package includes only the items listed. Other products not included. Lighting and monitor display settings may cause slight color variation between the image and actual item. Measurement allowance is +/- 1-3 cm.