The standard MTP brand coupler is what you'll find in the back of any MTP cassette. You'll also find them in a 4- or 6-pack MTP brand adapter panel. It essentially allows you to connect two MTP cable assemblies together (male and female). Standard MTP brand adapters are usually black whereas secure MTP brand couplers have several different colors in order to match connectors with specific couplers. If you want a longer MTP brand run, try using an coupler, but you'll need male (pinned) and female (unpinned) connectors to accomplish it.
Shuttered MTP brand couplers offer superior dust protection versus current products on the market. The MTP brand shuttered coupler has a spring loaded shutter door that is easy to operate and provides protection from airborne particulates, greatly reducing the time required for installation, testing and troubleshooting. A unique O-ring seal design keeps out signal degrading debris from the optics under the most extreme conditions.