The bottom bracket connects the cranks and frame, ensuring smooth power delivery. Mid BBs are the most common type on BMX bikes, followed by Spanish (more compact) and US BBs (for older frames). The key is compatibility with your crank axle diameter – usually 19, 22, or 24 mm. Bottom bracket sets consist of two sealed cartridge bearings, spacers, and, depending on the system, locknuts or press-fit rings. All bearings are sealed and designed for high loads. Whether you're replacing an old bottom bracket or building a new setup, you'll find the right bottom bracket for your BMX here.