The field of the invention is offset printing and the invention relates more particularly to printing presses used for printing newspapers or other large volume printing presses.  The presses are designed to use paper of a certain width.  Because of the high cost of paper, it has long been known that a substantial savings in paper costs can be accomplished by printing newspaper of a smaller width.  The cost of retrofitting a cylinder so that it can hold plate grippers more closely spaced has been very expensive, both because of press down time and labor costs.  Also, many presses have lockup mechanisms which are worn or otherwise deficient and there is a need for an improved plate lockup mechanism which can be retrofitted efficiently. 
It is an object of the present invention to provide a printing plate lockup mechanism which can be efficiently retrofitted in an existing cylinder of a printing press. 
The present invention is for a printing plate lockup mechanism for use with any web width, including width cut downs for attachment in a cylinder groove of a plate cylinder.  The groove has a floor into which holes have previously been drilled and tapped for holding the original printing plate lockup mechanism.  This is usually located in a removable bar described as a filler bar on most cylinders.  Rather than drilling and tapping any new holes, a base plate is secured against the groove 4 or onto a replaced filler bar with correct hole positioning.  The base plate has a plurality of gripper pivot rod grooves, a plurality of plate gripper cutouts and a plurality of base securement screw openings.  A plurality of plate grippers are held on gripper pivot rods positioned in the sets of gripper pivot rod grooves.  The pivot rods are held in the pivot rod grooves by rod retainers which are held by screws which are either screwed into the original drilled and tapped screws or in threaded openings in the base plate, or onto a replaced filler bar.  A plurality of thrust bars are used which have radius domes held and positioned by guide members held in openings in the base plate.  A pair of springs are held against the underside of the domes and against the groove floor to bias the plate grippers against the inwardly angled flanges of the plate cylinder groove.  The plate locating clips bridge the cylinder groove to allow rotation in either direction.  They may be positioned for any plate size and may be adjustable for changes in web width and are mounted to the base plate.