General Locksmithing Knowledge
Core concepts
General locksmithing knowledge is the vocabulary and theory layer that every other domain rests on. A candidate should be comfortable with the anatomy of a lock (cylinder, plug, shell, shear line, driver pins, key pins, springs, cam, tailpiece), the difference between a mortise, rim, and cylindrical lock, and the standard lock families: pin tumbler, wafer, disc, lever, and high-security designs. Know the common hand tools (plug follower, pin tweezers, tension wrenches, key gauges, depth and space keys) and what each is for. Understand basic door hardware terminology (backset, cross bore, edge bore, faceplate, strike, handing) and the difference between handed and non-handed hardware.
Traps to watch
Questions love to test the shear line: it is the boundary between plug and shell where the split between key and driver pins must sit when the correct key is inserted. Another trap is confusing the plug (the rotating part) with the cylinder (the housing assembly). Watch for handedness questions: a right-hand door swings inward toward the viewer when the door opens toward you. Also beware questions that mix up backset measurements (typically 2-3/8 or 2-3/4 inches) with cross-bore diameter.
Rule of thumb
When stuck on a terminology question, ask: does the part rotate, translate, or stay fixed? That single question usually resolves plug versus shell versus cam versus strike. For handing, stand on the outside and note which way the door swings and which side the hinges are on; hinge side plus swing direction fixes the hand.
Worked example
A question shows a pin tumbler cylinder and asks what happens when a key with one cut too shallow is inserted. The shallow cut leaves the key pin high, pushing its driver pin above the shear line, so the plug cannot rotate. The correct answer is that the driver pin binds across the shear line.