Features: aluminum alloy design, matted polishing, precised wire cutting, fully closed occlusion, not simple to slide teeth, and will not damage the bottom bracket Tool-a: suitable for using the bottom bracket with outside diameter of 44mm and 16 cogging This model is common specification of the bottom bracket (Bb51 / bb52 / bb70 / bb71bbr60 / mt800 / rs500 Tool-b: suitable for the bottom bracket with outside diameter of 46mm and 24 notches Process: heat, polishing, anodizing Suitable for bottom bracket with outer diameter 46mm 24 notches, Manufacturer: Msioytog