For Shimano direct mount cranks only Thick Thin Tooth Profile 10, 11 and 12 Speed Compatible 115 Degrees of Ovality Fully CNC Machined from 7075 Aluminium 30T Has a combination of 32T Increased Power Phase and 28T Dead Spot 32T Has a combination of 34T Increased Power Phase and 30T Dead Spot Burgtec recommend sticking to the current sized round ring that you are currently using when selecting your Oval size.