One thing many people have trouble with is identifying what fitting they need. Part of this is due to sizing, PVC pipe is sized (named) based on the inside diameter (ID) of the pipe. And to make matters works, the ID of pipe is approximate. It's not exact. 1" pipe can vary from .95" to 1.09". It's called "nominal" because the ID will average 1". (See our FAQ for more info on pipe sizes.) If you already have the pipe, just read the printing on it, it'll clearly say what size it is. You can also see our PVC pipe size chart. Once you know what size pipe you have, then you have to determine what fitting you need.
If you have pipe and want to connect it to another pipe, you need a couple or a union. A couple is glued together and can't be taken apart. A union still has pipe glued into either end, but it has a collar and 0-ring so that you can take it apart.
If you have a pipe and want to connect to a fitting, you just glue the pipe into the fitting. The fitting will be a slip socket.
If you have two fittings you want to glue together you use a short piece of pipe to go into the slip sockets of both fittings...
Or you have to either have one of the fittings be a street fitting (aka spigot fitting) like below:
If you want to connect a pipe to male threads, you need a female adapter. The female adapter will have a slip socket on one side and female pipe threads on the other. You teflon tape your existing male threads, then thread on the female adapter to the male threads, and then glue the pipe into the socket side of the female adapter. (See below.)
If you want to connect a pipe to female threads, you need a male adapter. The male adapter will have a slip socket on the one side and male pipe threads on the other. You teflon tape the male threads on the male adapter and then thread it into the female threads on the item you already have. Then you glue the pipe into the slip socket end of the male adapter. (See above and below.)
If you have a fitting (or other item) that has a slip socket and you want to put a pipe into it that's smaller than the socket you need a reducer bushing. The reducer bushing will spigot by slip socket. The spigot end will glue into the slip socket and the pipe will glue into the slip socket in the reducer bushing.
If the pipe you are putting is has threads, then you need a threaded reducer bushing. It will be spigot by female pipe threads (FPT).
If you have a fitting (or other item) that has a female pipe threads and you want to put a pipe into it that's smaller than the threads you need a reducer bushing. This reducer bushing will be MPT (male pipe threads) by slip socket. The MPT will thread into the female pipe threads of the fitting or item and the pipe will glue into the slip socket of the reducer bushing.
(No picture for this one yet.)
A nipple is a piece of pipe that has male pipe threads on both ends. If it's a "close nipple" that means the nipple is just long enough to thread each end into a fitting and the fittings will almost touch in the middle of the nipple. Nipples can be had in lengths from "close" to up to 60" long.
Other suggested reading:
