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 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.

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