PVC Couplers are the straight connectors used to connect two pieces of PVC. For example, when you are drilling with a two inch drillpipe and you add a section of pipe, it is a coupler that connects the old pipe with the new pipe. There are a couple of issues you need to be aware regarding couplers. The first deals excusively with two inch diameter couplers. This is the size of PVC that most will use as their drillpipe.
There are two sizes of two inch diameter PVC couplers. They are shown in the photos below.
TWO INCH DIAMETER COUPLERS
The longer, 2 7/8" PVC coupler on the left is the most common and it is the one you MUST use. The shorter, 1 7/8" PVC coupler on the right is not strong enough for our use. It will frequently break during the drilling process leaving a chunk or your drillpipe in the hole, unretrievable.
I apologize for the repetition but this is critical. You have to use the longer, stronger coupler. It won't normally be a problem to find as it is the more commonly available style coupler. The two inch coupler that is appropriate for our style of well drilling is approximately 2 7/8" long.
The second issue regarding couplers is inside vs. outside couplers. 99% of the couplers for sale are outside couplers, meaning they fit on the outside of the two pieces of PVC pipe they are connecting. Occasionally you might want to use an inside coupler so the pipe will have a slightly smaller maximum ouside diameter. For example, many people like to use inside couplers on their 1.25 inch wellscreen pipe. It slides just a little easier through their 2.00 inch drillpipe.
Below are pictures of both styles of two inch couplers. The coupler on the left is an outside coupler, the regular kind of coupler. On the right is an inside coupler.