 When the different length key pins are aligned at their tops by the insertion of the correspondingly cut key at their bases, the tops of the key pins and, consequently, the bases of the driver pins, form a shear line, so that the cylinder can be turned, rotating the key pins away from the driver pins.When no key or the wrong key is in the lock, pin misalignment prevents the cylinder from turning.To bump a lock, a person inserts a bump key into the key way one notch (pin) short of full insertion, then bumps the key inward to push it deeper into the key way.