A spring unit Cassette.
This Cassette is designed to increase the tension and performance of an old or weak lock. It converts unsprung handles to spring action. It is cut into the door below the back plate.
This product will work with most standard levers on Backplate. If your lock is not strong enough to prevent your new levers from drooping down, this cassette will help to alleviate the problem by supporting their weight. These can be fitted to one or both sides of the lock
priced per spring