The Shrink Ray is an item in Size Matters. It is a remnant of technomite society which can be used to shrink and grow objects. Ratchet and Clank use the device on many occasions, such as opening magnetic locks by shrinking Ratchet down to enter a lock and open it with the Grind Boots and OmniWrench to unlock them. It can also be used to enter technomite locations that are otherwise too small for Ratchet to access.
Grind Locks were small locks that could be accessed by using the Shrink Ray. Once inside a grind lock, Ratchet used grind boots to navigate a grind rail, and hit various targets along the way to disable force fields blocking the path. The objective was to get to the end of the grind rail without dying, by dodging or destroying obstacles, switching rails, and passing force fields. If completed successfully the lock would be unlocked and the door would open, Ratchet could then use the Shrink Ray to return to his normal size.
Otto Destruct also takes the device from Ratchet and uses it on himself in battle.
Behind the scenes
A bug allows the player to carry the Shrink Ray anywhere on Ratchet's hand, performed on Quodrona.