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). High-quality iron construction for durable, long-term outdoor use. Solid structure ensures reliable performance. Precisely designed with a 1/2 inch hole diameter for bicycle connection and 1 inch outer diameter for axle connection. Trailer connection hole is 1 inch in diameter. 12mm straight shaft requires adjustment. Replacement shaft features external threads. Ideal accessory for family biking, allowing your bicycle to tow a child or pet trailer. Enhances outdoor family activities. and high quality. Wear-resistant with excellent durability. Color: Black Material: Iron Package Contents: 2 x Traction Heads Note: Light and display differences may cause slight color variation between image and actual item. Measurement tolerance is +/- 1-3 cm.