Before you shop for a lockset for a door, be sure to make note of the following so the knob you buy will fit:

1) The door's thickness. Doors are typically either 1 3/8 inches or 1 3/4 inches thick. The thicker doors are usually, but not always, exterior models. Be sure to buy a lockset that will fit your door's thickness.

2) The "back set" dimension. The back set dimension is the measurement from the edge of the door to the center of the hole that is bored for the knob.

3) The type of lockset. Note whether the lockset is a cylindrical model or a mortise lockset.

4) The "handing" of the door. A door that opens toward you and has its knob on the left side is a left-hand door. A door that opens toward you and has its knob on the right side is a right-hand door. Though some locksets are reversible, those with curved levers instead of knobs are not.