For us DIY folks, and for a lot of industrial plants that use compressed air, one of the most common fittings we will use is the compressed air connector.
Their purpose is to mate with a coupler on an air supply line to allow, to allow a secure connections, and to allow compressed air to flow through to the air tools or air-using components.
Connectors are inexpensive devices, costing a dollar or two at most. For quick connection of your air tools, and rather than having to thread in a connector each time you wish to use the air tool, you may want to thread a connector into the supply port of every air tool you've got, thereby making them ready for use immediately.
By having a connector pre-installed in every air tool, changing your supply air from one air tool to another is simple and fast. Simply unplug one tool air connector from the air line coupler, and insert that of another air tool into the same coupler on the air line.
A typical connector is shown in the photo. An NPT male thread is on the left end. The right end (in this photo at least) is the part of the connector that plugs into the coupler. This is a manufacturer specific coupler shape, meaning that the connector shape must correspond to the coupler into which it is inserted.
Images of some common connector configurations follow.
Item 1 in the photo is a connector with a male NPT thread. After coating the male threads with thread sealant, this connector can be threaded into the mating female NPT threaded hole in an air tool.
The male NPT threaded connector is the most popular method of connecting an air tool to a compressed air supply. You will want to have an abundant supply of these on hand.
Item 2 shows the same connector with a female NPT thread, allowing this connector to be turned onto a male thread.
Item 3 (photo above) is the same connector again, but this one comes with a barbed connector.
The barbed connector is used by inserting the barb into the I.D. of an air hose. A gear clamp is placed on the outside of the hose which has been pushed up and over the barb, with the barb inserted fully inside the hose. When tightened, the gear clamp will exert force around the entire outside of the hose, compressing the hose wall against the barbs, and making a seal.
All three of the connectors formats above are industry standards. Two have standard NPT threads, and item 3 has a standard barb which is sized by its O.D. measurement.
For me, just a few of items 2 and 3 are enough for my air tool kit, as I use the male format (item 1) most frequently.