Bump key - no shoulder springs
Each set of compression springs has various lengths of steel compression spring -all tried and tested by us at ukkp's to make your bumping both faster and more effective.
The spring works by forcing the key to realign itself with the pins in the lock allowing you to strike it again quickly.
Spring Bumping has proven to be one of the best techniques available
There are at least 6-8 different springs provided in a pack