How can I visually tell the difference between a cylindrical and mortise lock?
A cylindrical lock has a round rose or escutcheon plate on the door face, with the lock mechanism contained in a cylindrical body that passes through the door. A mortise lock has a rectangular face plate on the door edge, with the lock body recessed into a pocket (mortise) in the door. When the door is open, you can see the rectangular edge of the mortise case in the door edge.
Why is a 161 prep called 'Turtle Prep'?
The 161 cylindrical prep has a large round cross bore on the door face and a smaller round edge bore, creating a profile that some in the industry compare to a turtle shape. CDF training materials use this visual reference to help specifiers quickly distinguish cylindrical preps from the rectangular mortise pocket of an 86 prep.
Is one lock type better than the other?
Neither type is universally better. Cylindrical locks are less expensive, easier to install, and suitable for most standard commercial applications. Mortise locks offer more functions, higher security, and greater durability in high-traffic environments. The choice depends on the application, security requirements, traffic level, and budget.
What happens if I order a door with a cylindrical prep but the building has mortise locks?
The door cannot accept the mortise locks. A mortise lock requires a rectangular pocket in the door edge that is not present in a cylindrical prep. A new door with the correct 86 mortise prep must be ordered. The original door cannot be field-modified to accept a mortise lock without compromising its structural integrity and voiding any fire rating.
Do fire-rated doors support both cylindrical and mortise locks?
Yes, fire-rated doors are available with either 161 cylindrical or 86 mortise preps. However, the specific lock model must be listed for use on fire-rated assemblies at the required rating — 20-minute, 45-minute, 60-minute, 90-minute, or 180-minute. The correct prep type must be specified at the time of order because the door is manufactured with the prep in place.
