An Overview of Cylindrical Locksets

Cylindrical locksets are the most common type of residential lockset in the United States.  This is due to both hardware costs and ease of installation.  This type of lockset came about in the 1930’s, but gained popularity in the 1950’s when Kwikset began producing a cylindrical lock that was much easier to install than those offered by its competitors.  The most common types of cylindrical locksets are key-in-knob locks, key-in-lever locks and cylindrical deadbolts.  Cylindrical locks are also common on commercial buildings, but are not seen on hollow aluminum doors due to their dimensions.

            A cylindrical lock is installed on a door by drilling a hole through both sides of the door for the lock assembly.  The location of this hole will vary depending on the lock’s backset.  Backset is the distance between the edge of the door and the center of the hole that is to be drilled for the lock assembly.  Some residential locksets feature an adjustable backset.  This allows the lock to be installed on a door that has already been drilled one of the two common backsets, which are 2 3/8” and 2 ¾”.  A second, smaller hole (usually 1” in diameter), is then drilled into the edge of the door until it intersects with the larger hole that has already been drilled.  A small mortise is then made for the latch faceplate using either a chisel or a router.  Some doors already come with these holes made.  These holes are known as a cross-bore.

Key-in-knob lock (bottom) and deadbolt (top) - View from unsecured side of door

            By contrast, it is much more difficult to produce a mortise pocket in the side of the door without the use of expensive specialized jigs and bits.  Most cylindrical locks, such as Kwikset knobs also allow a little more room for error than a mortise lock when it comes to the location of the holes drilled.  However, installation of either type of lock should only be done using a jig and never with the paper template that is often supplied with these locks—this template can easily become distorted when folded and if the door is beveled the holes on each side will be off.  A jig however allows both holes to line up in the same location and meet in the center of the door.

            The downside to cylindrical locksets is that they are generally less secure than mortise locks.  Also, excluding a few rare exceptions (e.g. Schlage G-Series) cylindrical deadbolts and key-in-knob locks are not interconnected.  This means that if you need to exit a room and the deadbolt is locked, you must rotate the inside thumb turn first and then rotate the inside handle in order to egress.  By contrast, most mortise locks today are interconnected allowing you to simply rotate the inside handle and open the door even if the deadbolt has been thrown.  For this reason cylindrical deadbolts are virtually nonexistent in commercial buildings.

            Ultimately, it comes down to cost versus quality.  Mortise locks are typically a better investment for a commercial building where doors see frequent usage, or the front door to a residence, where the owner wishes to preserve the original styling.  Also, if a door has already been fitted with a mortise lock, converting to a cylindrical lockset is generally not practical, as the entire mortise pocket has to be filled in as to prevent damage to the door that would otherwise result from the hollow cavity.  Therefore, if the mortise lock on an interior door to an older home starts to experience issues, it is advisable to either have it repaired, or track down a replacement lockset as opposed to running out to a big-box retailer and grabbing the first doorknob you see.