In buildings, and more particularly within communications connection closets in buildings, the various transmission media are connected to each other and to incoming and outgoing lines by means connectors mounted on patch panels.  As it is most commonly configured today, a patch panel comprises a plate having arrays of openings therein, the openings usually being substantially square in shape.  Thus the panel has become standardized, and numerous arrangements for mounting connectors to the panel are in use.  In U.S. Pat.  No.  5,238,426 of Arnett, there is shown such a patch panel and adapters for mounting connectors within the openings.  As is shown in that patent, the connectors, or jacks, are generally square in shape and are intended for use with electrical signal systems.  In such electrical systems, these jacks are, for the most part, standardized throughout the industry, as are the panels, themselves, with their arrays of square holes.  The arrangement shown in the Arnett patent comprises a panel, a connector or jack and an adapter for mounting the connector to the panel in one of the square holes thereof.  The adapter receives the connector and locks it in place by means of resilient tabs on the connector engaging front and rear surfaces of a bridging portion on the adapter.  The adapter has resilient arms, each arm having two spaced wedge shaped detent members which engage the front and rear surfaces of the panel to lock the connector-adapter assembly in place.  Such an arrangement allows any of a number of types of electrical connectors to be secured to the panel by securing the connector to the adapter which, in turn, is secured to the plate. 
The mounting of optical fiber connectors to a panel presents numerous problems, some of which, at least, stem from the fact that there are numerous types of optical fiber connectors in use today which are incompatible with each other and which vary as to size, shape, and method of connection.  Because of these variations, it is often difficult to fabricate a patch panel assembly.  In U.S. Pat.  No.  5,274,729 of King et al.,  the lack of standardization among the different types of connectors and the concomitant problems of connection are readily apparent.  In the King et al.  patent, a panel is formed with a plurality of different shaped holes therein for accommodating the several types of connectors, among which are the ST, SC, and FC optical connectors.  Different adapters are provided for each type of connectors, each being designed to fit within one of the holes in the panel specifically shaped for the type of connector and for the particular adapter.  Such an arrangement requires a panel in which the number of holes of a particular shape is limited, thereby limiting the number of one particular type of optical fiber connector that can be used with the panel. 
An optical fiber connector must be capable of joining two optical fibers with a minimum of insertion loss and it must be mechanically stable and provide protection to the junction between the optical fibers.  One of the most commonly used connectors which satisfies these requirements is the SC connector, the general industry acceptance of which is increasing rapidly.  Such a connector, in an improved version thereof, is shown and described in U.S. Pat.  No.  5,212,752 of Stephenson et al.  An SC connector is connected to another SC connector through a coupler to which each SC connector is assembled by linear motion only.  As shown in the Stephenson et at.  patent, an SC connector includes a ferrule assembly including a barrel having a collar at one end and an optical fiber terminating ferrule projecting from the barrel.  The ferrule assembly is disposed in a plug frame such that an end portion of the ferrule projects from one end of the frame.  The plug frame is configured to snap lock into grip member, and the grip is inserted into one side of the coupler and locked thereto, while the corresponding grip of another SC connector is inserted into the other side of the coupler and locked.  The coupler is dimensioned such that when the two connectors are inserted therein, the ends of the ferrule abut each other to form a low insertion loss optical connection.  Also, the ferrules in the Stephenson et at.  coupler are spring loaded to allow for slight variations in dimensions, among other things. 
Because the SC connector is compact and easily installable in the field, it has become common to use a duplex coupler which is capable of optically coupling two pairs of optical fibers in a side by side arrangement, rather than using two separate couplers, thereby reducing the number of adapters required.  However, at present, there is no adapter or collar for mounting a duplex coupler to a panel having the standard array of substantially square holes therein.  In addition, the standard duplex SC coupler available today is designed to be snap locked into an opening in a panel, for example, that is approximately one-sixteenth of an inch thick, but the panels most commonly used today, such as the AT&T M1000 Multi-Max. RTM.  panel, are approximately one-eighth of an inch thick.  Thus, a collar or adapter is needed that adapts the rectangularly shaped duplex coupler to a standard one-eighth inch thick plate having an array of substantially square holes. 
When the collar or adapter is snap fitted into place within a hole in the panel, there exists the unwanted possibility of an inadvertent release of the snap locks, thereby allowing the collar to fall off of the panel, or at least, out of the hole.  In an electrical arrangement, this is not a serious problem, although it is undesirable.  However, with optical fiber coupling, any dislocation of the coupler assembly on the panel can have serious consequences, including an interruption of service because of a disconnection.  It is desirable, therefore, to lock the adapter or collar to the panel in such a way that inadvertent release of the lock or locks cannot occur.