Sparrows circular spring loaded Tension Wheel in brass and black.
The Tension wheel is a unique beast and when properly used it is a handy tool.
When improperly used it leads to frustration and surly language In order to use it effectively the lock needs to be either mounted or in a vice.
Light tension - seriously light tension - Start in the half bar section and rake the lock. Then release the tension. If no pins dropped Increase the tension another half. If you could hear pins drop then you are in the right tension zone. Apply that same amount of tension and begin picking. It also helps when teaching lock picking - tension control can be difficult to describe to a student.
With a marked Wheel you can see the amount of tension being applied and recommend a Zone. This makes some of the initial learning a bit easier.
Another area where the Tension wheel is extremely useful is electric picks. Some use it exclusively for electric picks and snap guns.
Don't throw out the rest of your tension wrenches or bars - the wheel is just another tool. It shines in some areas and induces surly language in others