Note : It's not fit for old version mid motor. Please kindly contact us before order. Thank you.Product Description:The nylon primary reduction gear is one of the weak links in the Bafang BBSHD system.If you apply too much power while in the wrong gear you can strip them creating a problem referred in the community as "peanut butter gear".Nylon Gear is necessary because if steel gears were used the BBSHD would be very noisy.