Fixes into the frame in place of the rear wheel, being held in place by the bikes thru axle, keeping the chain tensioned & held away from the frame. The chain sits in a roller, which allows the cranks to be rotated, making this ideal to be used when cleaning the chain & 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