Fixes into the frame in place of the rear wheel, being held in place by the bikes thru axle, keeping the chain tensioned and held away from the frame. The chain sits in a roller, which allows the cranks to be rotated, making this ideal for use when cleaning the chain and derailleur. It can also be adjusted to fit dropout spacings from 135mm to 150mm, meaning that the rear of the frame cannot be compressed or damaged during transport