An Overview of Cylindrical Deadbolts

The bolt is the heart of the deadbolt. Bolts will vary in diameter, material, construction, length and backset. Smaller bolts will generally be found on lower grade residential locks.

The most common type of deadbolt in use today is the auxiliary cylindrical (bored) deadbolt. The deadbolt is usually installed above and in addition to an existing knob or lever, cylindrical or mortise lock.

The installation is accomplished by drilling two primary holes in the door; one edge-bore hole to accept the bolt mechanism and one cross-bore hole to allow the main housing to fit into the door.

The most common door prep uses a two and one-eighth inch cross-bore with a one-inch edge-bore. Another popular installation uses a one and one-half inch cross-bore with a one inch or seven-eighths inch edge-bore.

Adapter plates are included in many deadbolts designed for the smaller cutout to allow them to be used in the two and one-eighth cross-bore.

Like most other security hardware, deadbolts are usually graded to indicate their intended usage and application.

Grade 1 is considered Heavy-Duty Commercial, Grade 2 is considered Standard Duty Commercial and/or Heavy Duty Residential while Grade 3 is Standard Duty Residential and intended for residential use only. There are other deadbolts that would be considered Grade 4 Light Duty Residential, and others that are not rated at all. Be aware that quality does not usually come cheap.

Some deadbolt lock packaging will use the words ‘Heavy Duty' but the lock may not even be rated. Regardless of words on the box, when no rating is specified, consider it Grade 3 or 4 at best. Generally the heavier duty the lock is, the stronger the components and materials used in its construction. The lock manufacturer pays for the testing procedure and if it has a Grade 1, 2, or 3 rating, the manufacturer would want the buying public to know.

Common cylindrical deadbolts have four major components; outer trim, inner trim, bolt mechanism and strike plate.



The outer trim consists of a keyed cylinder, a trim ring or rings and sometimes an adapter plate. On Grade 1 deadbolts the outer trim ring is either a solid machined metal ring or a solid inner ring with an architectural cover. The solid ring provides protection from attack with a hammer and is free-spinning to prevent wrenching the cylinder to gain entry.

Grade 2 deadbolts may use a semi-solid filler ring for protection and Grade 3 locks may just use a hollow metal ring to hold the cylinder body.

The good news is that the cost is reduced with each reduction in grade. The bad news is the security and usually the endurance levels are also reduced.

The standard deadbolt uses a keyed cylinder on the exterior. This cylinder can be anything from the most common residential keyways to high security cylinders. Some deadbolt designs allow you to interchange a different keyway or substitute an entire knob/lever type cylinder with the proper deadbolt tailpiece.

High security deadbolts will offer hard plate or ball bearing components that provide protection from drilling for the shear line or drilling the mounting screws out to gain entry. Inexpensive deadbolts do not offer these features.

Some specialty deadbolts designed for use in rest rooms don't have an outside cylinder. There is a flat plate with an indicator window showing either a red or green background, and a message such as “Occupied/Vacant” or “In Use/Open”.

Other deadbolts are one-sided and will have a plain flat plate or nothing at all on the exterior of the door. These are meant to be used when no access is desired by any means when the door is locked.

Because a deadbolt must be locked after the door is closed, each time you leave, you must turn the key in the outer cylinder to secure the door. The only exception is a unique deadbolt feature that allows the user the spin the outer trim ring, throwing the bolt upon exit. Since many people are too rushed or lazy to take the time to actually lock the door when leaving, this feature may be a great way to be sure the door gets locked.



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