a compressor unit for a file unit , wherein there is provided a compressor body which has a substantially vertical plate part which extends partially across the file unit and is positionable adjacent the rear of a row of documents . the compressor body mounts thereon a brake plate which is slidably accommodated within a confined channel which extends longitudinally along a wall of the file unit . a pressure plate is slidably mounted on the compressor body and has a foot portion which overlies the brake plate so that braking flanges as associated with the fixed channel are interposed therebetween . a manually - releasable compression linkage is movably mounted on the compressor body and has wedging surfaces which cooperate with the pressure plate for causing the pressure plate and brake plate to be moved toward one another to frictionally grip the braking flanges therebetween .