A chopper for chopping items such as fibers, fiber strands, ribbon, etc. by passing the items continuously in a loose, unwound, condition through the nip of a blade roll and a backup roll having a working layer on its outer periphery. The chopper of the present invention uses one or more rolls that are radially expandable and retractable to replace the blade roll and/or the backup roll on the prior art choppers so that worn blades and/or a worn working layer can be more quickly and more easily replaced with a new or repaired working layer or blade holder containing sharp blades. The chopper of the present invention eliminates the need to carry large, heavy, awkward rolls through the fiber forming rooms or areas where the items are being chopped and also to transport such rolls back and forth to the location where they are being rebuilt. Instead only lightweight working layers or blade holders are carried to and from the choppers and such are installed on the choppers with much reduced downtime than heretofore necessary.