The On Track BB Cupset Sealed 51.4mm O.D is a durable, one-piece sealed bottom bracket designed for bikes with small one-piece cranks. Featuring a 51.4mm outer diameter, it ensures a secure and stable fit. The sealed design provides smooth, long-lasting performance by preventing dirt and moisture from entering, making it ideal for consistent riding. Compatible with 5/16" x 9mm sizes, this bottom bracket cup set is a reliable choice for high-quality bike maintenance.