Door Locks, Deadbolts and Lock Cylinders

Measure the door before choosing the lock

Locks fit holes that already exist. Measure the backset, the distance from the door edge to the center of the main bore; 2-3/8 and 2-3/4 inches are the two common values, and many locks can adjust between them. Then measure door thickness and the bore diameter, often 2-1/8 inches. A cylinder or rim lock has a tailpiece or bolt length that must reach the latch through your door, so thickness matters as much as hole size.

Rim cylinders sit on the surface of the door and work with a rim lock or deadlock, while mortise cylinders screw into a lock body cut into the door's edge. Titles list a cylinder's length or its tailpiece size in inches, such as 2 inch or 2-1/2 inch. Keyway, the key profile, must match the lock or the system you already use, so note it before choosing a replacement cylinder.

Single or double cylinder, and what the grade tells you

A single-cylinder deadbolt takes a key outside and a thumbturn inside; a double-cylinder needs a key on both sides, which blocks reaching through glass but can trap people in a fire, so some building codes restrict it. Grades rate strength and durability: Grade 1 is the heaviest duty, then 2 and 3. Terms like jimmy-proof deadlock describe a bolt that resists prying, and keyed alike sets let several locks share one key.

Questions about Door Locks, Deadbolts and Lock Cylinders

Can I rekey a lock instead of replacing it?

Many pin-tumbler cylinders can be rekeyed by a locksmith or with a kit from the same maker, which changes the working key without replacing the lock. Restricted high-security cylinders usually need the maker's key control.

What does keyed alike mean?

Locks that are keyed alike open with the same key, so a front door, back door and gate need one key. Keyed different locks each need their own. Check the listing for the wording, since most single locks are keyed different.

Are push-button mechanical locks secure?

They suit sheds, utility rooms and internal doors where you want keyless entry without batteries. Code length and the grade vary, so check a stated security grade for outside doors, and change the code from time to time. Heavy-duty entries use a deadbolt.