magari le BOR funzionano come le XX
leggi qui :
29ER : Ultra-Light, CNC-machined chainrings for 29er MTB for 2x10 between 16 - 56 grams : BCD 104 and 64 mm with thread in big chainring
This system corresponds to the SRAM XX-attachment principle, but on a smaller bolt cycle diametre. The large rings each have the same thread as XX chainrings. They can be mounted on 2x10 spiders with BCD104/64, as they exist from SRAM (X-0) or Specialized. The rings can also be mounted to regular 3x10 spiders!