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There are a wide variety of different types of mortise locks and rim locks, found on both residential and commercial doors. It would be impossible to cover all of the different types of these locks and their variations in one article. 

 However these locks have something in common. They are very routinely mistaken for each other when someone is practicing size up on these doors. Now there are many key features that can be studied and identified from the outside that would allow you to identify them far before you pull the cylinder. It does take some practice and attention to detail to pick up on these, so that you can efficiently identify them a majority of the time. We may make that an article for another day, for now we feel it is important to cover the bottom line of what needs to be identified to get in these locks.

The above picture is a good example where we may run across these types of locks. This door has a mortise cylinder and a rim cylinder. The top cylinder is a dummy lock that does not operate anything. Since we have the luxury of glass and no conditions behind it, we can easily identify these locks. We see the bars across the door behind the glass which line up with the bottom cylinder. That is our indicator that this will be a rim cylinder operating a panic bar (rim lock). When we look at the cylinder above we can expect this to be our mortise cylinder which is more than likely set in a adams rite mortise lock with a deadlatch. This is the most common lock found in these doors, and if you only have one cylinder showing it is probably this type of lock.

If we decide thru-the-lock is the tactic of choice and we decide to pull the cylinder, there are a few things for us to look at. If we did not know what type of lock we were dealing with before we pulled the cylinder, we can immediately identify it after it is removed. By taking a quick look at the cylinder it will inform us of the type of lock we are going to trip and what end of our tool we will need to use (Either the angled end or the straight end).

Pictured above are the two types of cylinders, the mortise is the dark colored cylinder and the rim is the gold cylinder. Even though these looked almost identical from the outside, you can now see significant differences. The mortise cylinder has the threaded body which holds it in place with a set screw whereas the rim cylinder has the two mounting bolts which connects to a thin metal plate on the back of the door. More importantly we can see the differences in their mechanisms. The mortise cylinder has the cam on the backside which rotates around as the key is turned allowing the small point on the cam to activate the lock. Next when you look at the rim cylinder you can see it has a stem which looks similar to the flat blade of a screw driver. This also turns and activates the lock. The main characteristic to remember from these above pictures is where the action of the lock is taking place. The mortise is activated downward and inside the door. The rim is activated straight back and on the backside of the door.

Here is a break down of each cylinder and lock by themselves.

You can see the mortise cylinder next to the commonly found Adams Rite Mortise Lock. By recognizing the previously discuss parts of this lock like the cam, we know we will be using the angled end of our tool to activate the pin below where the cylinder sat.
This picture is a good view of the mechanism behind mortise cylinders. A good landmark to remember is the open cutout on that arm that resembles a lightbulb. If you remember that cutout looks exactly like the shape of the cam on the back of the lock, and it also points to the exact spot we should place our tool to activate the button that can be seen in this picture. Once the button is depressed we will move the mechanism towards the jamb side of the door to release the latch. Not all mortise locks activate with the exact motion but a large majority of the do have a pin that needs depressed before the action can be made.

Next you can see the rim cylinder as if it had just been pulled.
 

The key points that we see here are the mounting bolts and the long stem. This reminds us that our lock will be activated straight in on the backside of the door. You can see the tell-tale plus sign on the lock, this is where the stem fits in to activate the lock. Many of these are simple quarter turn locks that is easily done with a flat screw driver.

These locks can be easy to over think, and sometimes you try and use too much force due to the small simple action that typically throws these locks. After you give the lock a quarter turn or until you meet resistance, try the thumb latch if it has one, or pull on the door to make sure you haven’t just unlocked the door but forgot to pull it open before the latch went back into place. This will tend to happen on panic hardware as the latch is more than likely spring-loaded in the locked position.

The bottom line out of all of this is: Rim = Stem= Straight end of the tool
                                                                        Mortise=Cam= Angled end of the tool

To wrap up we have a couple pictures showing you some different ways that mortise cylinders and rim cylinders may present themselves in the commercial setting.