19mm

Specifications: Shell Width: 68mmThis is the standard width for most BMX, cruiser, and some mountain bike bottom bracket shells. It determines the spacing between the two sides of the bottom bracket. Spindle Type: 19mmThe spindle diameter is 19mm, which is compatible with most 3-piece cranks designed for this size. The spindle is the part of the crankset that passes through the bottom bracket. Cup Type: Press Fit 51mmThe bottom bracket uses a press-fit system with cups that have a 51mm diameter, which is typical for American bottom bracket shells. The cups are pressed into the frame's bottom bracket shell rather than threaded. Interface: AmericanThis refers to the type of bottom bracket shell used. The American bottom bracket shell is larger and typically found on BMX, cruiser, and some older style bikes. It accommodates press-fit cups rather than the threaded types seen in other standards like BSA/English. Bearings: Sealed 41mmThe bearings are 41mm in diameter and sealed, providing protection against dirt, water, and debris. Sealed bearings require less maintenance and offer smoother performance compared to open bearings. Material: AlloyThe bottom bracket cups and other components are made from alloy, which is lightweight and durable, providing a balance between strength and weight. Color: BlackThe bottom bracket set is finished in black, giving it a sleek and modern look that complements most bike color schemes. Conversion Capability:This bottom bracket set is designed to convert an American-style 68mm bottom bracket shell to fit a 3-piece crank with a 19mm spindle. This allows bikes with an older or BMX-style bottom bracket to be upgraded with more modern cranksets.Brand and Manufacturer: Brand: AltaLineAltaLine is known for producing high-quality bicycle components, particularly for custom, BMX, and lowrider bikes. Manufacturer: F&R Cycle Inc.F&R Cycle Inc. is the manufacturer that specializes in bike parts and accessories, catering to the needs of custom bike builders and enthusiasts.