An Overview of Cylindrical Deadbolts

Nov. 1, 2007
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.


The majority of deadbolts use an inner trim consisting of a thumb-turn. These single-sided deadbolts are locked or unlocked by key from the outside and by thumb-turn from the inside. When the door is locked from the inside, the key will provide access. The key and thumb-turn are independent and either one will work the lock at any time.

Double-sided deadbolts have a keyed cylinder on the interior of the door in place of a thumb-turn. Special considerations need to be taken when installing a double-cylinder deadbolt.

The concept of the double-sided deadbolt is that when used on a door with a window or with glass sidelights, someone can't break the glass and reach in to gain entry. In an extreme case, double cylinder locks on all of the doors would force a person back out of the window used to gain entry and may prevent them from stealing large bulky items.

Because a key is required to lock or unlock the door from either side, safety is a factor. In the event of a fire, someone running to a locked door must have the key to egress the building. Contact your local authority having jurisdiction before installing a double-sided deadbolt on a commercial building.

Running around at night in an emergency screaming “Where are my keys!” is not the best scenario for survival. One residential solution is to have an extra key on hand. This key is hung up near the door or is left inserted in the inside cylinder at night while someone is at home. When the key is left in the inside cylinder, it operates the same as a single-sided lock.  

Since this ‘extra key' is vulnerable to someone borrowing it without your knowledge, one trick is to ‘short cut' the key. In other words if the outer cylinder is a six pin key, cut the interior key on a five pin blank and only key the inside cylinder up to five pins.

That way the key only works on the inner cylinder. The regular key works both sides of the door but the extra key only works on the inside. If it disappears during a party, you can be assured that no one can use it to gain entry. Simple master keying of the inside cylinder to a separate key accomplishes the same thing.

Another solution to the same problem is the hybrid deadbolt, combining the features and benefits of both single and double cylinder deadbolts. The manufacturer accomplished this benefit with a special ‘thumb-turn key'. The inner lock of a double cylinder deadbolt operates as such until a specially cut key blank is inserted. This blank has a cut key blade mated to a thumb turn lever. When inserted, the special key looks and operates like a standard single-cylinder lock.

In fact, the key can't be removed again until the outer cylinder has a key inserted and turned to a specific position. This activates a small cam piece that allows removal of the inner thumb-turn key. Once removed the lock looks and operates as a standard double-cylinder deadbolt. Again, the special key only operates in the inner cylinder and is ineffective in the outer cylinder.

Note: Anytime you consider a double-cylinder deadbolt as a security solution, be aware that some Life Safety codes may prohibit them. The local AHJ (Authority Having Jurisdiction) can furnish specific codes and laws in your area.


The bolt is the heart of the deadbolt. Bolts will vary in diameter, material, construction, length and backset. The diameter of the bolt will vary from about three-quarters of an inch to one inch. Smaller bolts will generally be found on lower grade residential locks.

Heavy duty locks will feature larger diameter bolts, many will incorporate an anti-saw rod or rods embedded into the body of the bolt to help resist a saw attack. Some rods are identifiable by looking at the leading edge of the deadbolt, others are imbedded inside the bolt, out of sight.

The length of the bolt is also important. Some deadbolt locks will use a smaller shorter five-eighths inch bolt. Others including many lighter duty locks will use a one inch bolt. The longer bolt will provide more security against a spreading attack where a door and frame is spread apart until the bolt is released from the strike pocket.

Materials used in the bolt will vary from cast, powdered metal to machined stainless steel. As with other features, price increases with the quality of the materials used.

Finally, the backset of the deadbolt must match the door preparation.

The two most common deadbolt applications are two and three-eighths and two and three-quarters of an inch backset. With this in mind, many manufacturers have designed deadbolt mechanisms that are adjustable between the two measurements.

Another bolt-related design change is a metal shield designed to cover the top edge of the deadbolt when it is in use. The metal shield is attached to the lock housing and prevents someone from using a sharp pointed instrument from attacking the activating finger of the deadbolt.

In this type of attack, an awl or ice pick is pushed through the door, just above the outer deadbolt trim ring. The tool can be used to manipulate the activating finger to a neutral position allowing the bolt to be withdrawn, unlocking the door. The shield covers this sensitive area from attack.


Often overlooked during the installation is the strike plate. When an existing deadbolt is replaced, the existing strike is often re-used if is properly aligned and the bolt throws and retracts smoothly.

The problem with this habit is that you may be short-changing the customer on security. Most Grade 1 and 2 deadbolts are now packaged with a security or heavy duty strike plate and extra long (3” long) screws in order to secure the strike plate into the inner stud of a wooden frame. Other over-sized and aftermarket security strikes are available as well. All are intended to increase security.

If the gap between the lock side of the door and the jamb is large, surface mount the strike plate. Explain to the customer that by surface mounting the strike plate, the deadbolt has more material to push against provided a more secure installation.


Mortise locks may incorporate deadbolts in the mechanism, but they aren't considered auxiliary deadbolts.

Some cylindrical deadbolts are incorporated into a knob or lever lock by the trim. Usually these appear to be a separate knob and deadbolt from the exterior, but are interconnected with an interior trim plate. When the deadbolt is locked, turning the inside knob retracts both the dead latch and deadbolt in one motion.

East Coast locksmiths still deal with a lot of surface-mounted or rim deadbolts. These are usually installed above the knob or mortise lock and use a rim cylinder on the outside and a surface-mounted deadbolt lock body with a thumb turn for inside control. The bolt throws into a surface-mounted strike.

The final consideration when selling and installing a deadbolt lock of any type is to look at the door and the area surrounding the jamb. If the door is not solid core, a deadbolt will probably not provide the desired security. A single pane window large enough for a person to walk through adjacent to the door lessens security dramatically. A non-graded deadbolt with a 5/8” throw is probably not worth installing. A quality deadbolt lock properly installed onto a solid core door can provide the end user with many years of confidence and security. Remember the cost of residence must be considered when selling a deadbolt.