Different Types of Bottom Brackets Available
The original Bottom Bracket for BMX also referred to as a Pro size. The bearing rests in a cup that is pressed into the frame. The bearings are large and durable, but typically heavier than other types. 2" (50.8mm).
European Bottom Brackets use small cups that thread into the frame, making installation very easy. Since the bearings are small, most European Bottom Bracket kits use four bearings to spread the load.
Spanish Bottom Brackets use a bearing that presses directly into the frame without the use of a cup for a clean, flush look. Spanish bearings are larger than the European bearings, but still smaller than the American bearings. 1-7/16" (36.5mm).
Mid Bottom Brackets use an American sized bearing that presses directly into the frame without the use of a cup, leaving a flush fit. The bearings are strong, but slightly heavier than Spanish bearings. 1-5/8" (41.2mm).