Description: Durable Material: Made of premium chromium-molybdenum steel material, high performance and for heat resistance, long service life. Special Design: High-precision internal thread to ensure close connection with the hub and stable rotation. Useful Function: The flywheel is lightweight and compact, and can be easily removed or installed on the bicycle. Fine Workmanship: Wonderful workmanship of our product ensures a delicate details and a good using experience. Meaningful Tool: When you need to use them in a way for a long time, the product will quickly become your good helper. Specification: Color: As shown as picture. Material: Chromium-molybdenum Steel. Size: Approx. 8.00*6.00*1.00cm/3.15*2.36*0.39in. Diameter of 11T: 4.2cm. Diameter of 12T: about 5cm. Diameter of 13T: about 5.3cm. Note: There might be a few color distortions due to different computer resolutions. There might be a slight error due to different hand measurements. Package Includes: 1 Piece Freewheel Part Accessory. Durable Material: Made of premium chromium-molybdenum steel material, high performance and for heat resistance, long service life. Special Design: High-precision internal thread to ensure close connection with the hub and stable rotation. Useful Function: The flywheel is lightweight and compact, and can be easily removed or installed on the bicycle. Fine Workmanship: Wonderful workmanship of our product ensures a delicate details and a good using experience Meaningful Tool: When you need to use them in a way for a long time, the product will quickly become your good helper