Features: brand new and high quality The built-in push wheel is basically suitable for most folding bikes. It can be used with or without air cylinders. No tools are required. It is directly put on the for seat tube and installed quickly. After being suitable for folding bicycles, the booster is installed on the seatpost to help push and lift. 360°universal rotation, free direction control, compact and light. The hidden auxiliary wheel is installed inside the folding bicycle seatpost, which is convenient and quick, and does not affect the disassembly of the bicycle. It is not only suitable for folding bicycles, but also can be installed on round pipes with inner diameters of 28-32mm/1.10-1.26inch, or 25-44mm/0.98-1.73inch outer pipes, such as tables, hangers or shelves. Specifications: Material: Metal Color: Silver/Black Size: Approx. 3.5x6.9cm/1.38x2.72inch Package Includes: 1x Auxiliary Roller Wheel note: 1.Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item.