A doorknob or lever handle will have one of the following:
- Zero keyholes (passage or privacy function)
- One keyhole (keyed entry or storeroom function)
- Two keyholes (usually only in commercial, school, or industrial functions).
A deadbolt will be either:
- Single cylinder with ONE keyhole outside and a thumb-turn on the inside
- Double cylinder with TWO keyholes, one inside and one outside.
Therefore an average door with a knob or lever and a deadbolt may have 1, 2, or 3 keyholes on that door.