Parallel Arm Door Closer Options
Parallel arm closers are available with many control options. In this brief article we'll review what some of those arm options are and the benefits of each.
Parallel door closers are different than "regular" arm closers because of the way they are mounted to the door and the way the arms are made. The main distinction between the two types of closers are that the parallel arm closer will be mounted on the push side of the door with the end of the arm being installed to the soffit of the frame. The regular arm closer is mounted on the pull side of the door with the end of the arm being installed on the face of the frame. (Read this previous blog post to learn more about the difference between parallel arm closers vs. regular arm closers)
Parallel arms are available with many more controls than the regular arm closers. Here are the basic options available from most door closer manufacturers.
The thumbturn style hold open is generally used in conjunction with the built-in door stops. At the point where the door is stopped by the built-in door stop, there is some sort of ball and catcher that can be engaged and disengaged by the thumbturn. The thumbturn will have a small concave projection that holds onto a ball that is inset in the shoe. 
(Keeping the thumbturn engaged while swinging the door open and closed is not recommended. You should allows disengage the thumbturn hold open before closing the door so that the concave projection lasts longer.)
Hold Open Arm
Hold open parallel arms can be either a friction nut style hold open or a thumbturn type hold open. The friction nut can be set so that at a certain degree of opening the door will hold open. You can adjust where the friction nut will tighten and hold the door.The thumbturn style hold open is generally used in conjunction with the built-in door stops. At the point where the door is stopped by the built-in door stop, there is some sort of ball and catcher that can be engaged and disengaged by the thumbturn. The thumbturn will have a small concave projection that holds onto a ball that is inset in the shoe. (Keeping the thumbturn engaged while swinging the door open and closed is not recommended. You should allows disengage the thumbturn hold open before closing the door so that the concave projection lasts longer.)
Extra-duty Parallel Arm Closer
Parallel arms can be specified to have a heavy-duty arm. This heavier-duty arm is made from more durable material and can be used on higher traffic doors where more abuse can be expected. Extra-duty arms are meant to last longer than the standard-duty arm that is supplied standard with the door closer.
Built-in Door Stop Arm
A parallel arm can be made with a built-in door stop. This door stop is usually a metal post that is secured into the shoe and acts as a "dead stop" for the door. As the door swings open, the arm comes in contact with this door stop and prevents the door from swinging any further.
Built-in Spring Door Stop Arm
The built-in spring door stop is similar to the standard built-in stop except that the spring acts as a "catch" for the door. This spring stop will have some "give" to it so that the door doesn't stop immediately. It is easier on the closer and the door to have this spring stop installed.