Pictures of Thumbwheels and Cams in Disassembled Lock
In the picture above, the four thumbwheels and four cams, one to the right of each thumbwheel, are visible. The flat edges of all four cams are toward the bottom of the lock, in the positions where the feeler inserts deepest.

Normally, the cams are tight against the thumbwheels, as is the cam next to the leftmost thumbwheel is in the picture. The spring which pushes the cams against the thumbwheels is missing from this lock, allowing the cams to move to the right. The cam next to the rightmost thumbwheel has pulled away furthest from its thumbwheel.

The combination change tool pushes the cams to the right, disengenging them from the thumbwheels. The thumbwheels can then be moved to the new combination while the cam flat edges remain aligned under the pawl. When the combination change tool is removed, a spring pushes the cams back, re-engaging them with the thumbwheels. The cams again move when the thumbwheels are turned. The new combination now aligns the flat edges of the cams under the pawl, allowing the lock to open.
In this picture, the flat edges of the cams are visible next to the two thumbwheels on the left. The round edges of cams are visible next to the two thumbwheels on the right. The cam for the tens digit thumbwheel is pulled away from the thumbwheel. The cam for the ones digit is close to the thumbwheel. (Since a spring pushes the cams tight against the thumbwheels, the feeler won't ordinarily slip between the cam and thumbwheel.)

The feeler is used to line up the cam flat edges toward the bottom of the lock. To open the lock, each thumbwheel must be turned a quarter turn up to move the corresponding flat edge under a tong on the pawl. The ends of the tongs are the bright squares above each cam.

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