The stitching unit H-15 has been developed for side-wire-stitching of folded sections and single sheets for linking with a perfect binder. The unit is suited to be linked to perfect binders: City, Master or Champion. Optionally also for later linking to already existing perfect binders as City, Master, Champion, Golf 6001 and Master 6501. The feasibility of later retrofitting must be checked on case-by-case basis.