Bicycle trailer coupler compatibility: suitable for most bicycles as well as disc brakes and and instep brand trailers. It's not for style dropouts. For QR shaft and 12 mm (outer diameter) solid shaft, about equal to 0.48 inch). High quality material: high quality iron, solid structure, excellent structure, outdoor long-term use of high-quality trailer connector. Precise design: the diameter of the hole connected to the bicycle is 1 / 2 inch, and the outer diameter of the part connected to the axle is 1 inch. The hole in the trailer is 1 inch in diameter. 12mm straight shaft needs to be adjusted straight shaft. This replacement shaft has external threads. Family fun: additional trailer coupler accessories connector, family bicycle can be equipped to tow children's trailer, your child or pet will enjoy the fun of riding a bicycle. 100% Band new and high quality:High Wear-resistant and excellent durability. Colour: black Material: iron Package Contents: 2 x traction heads Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.