A nipple is essentially a short piece of pipe with male threads at both ends. It is one of the most common fittings you will see, often used to connect two female fittings or attach pipes to appliances like water heaters. The part bearing one or more protrusions, or which fits inside the other, is designated male, while the one with the corresponding indentations, or fitting outside the other, is designated female. Fitting - can refer to either a Plug or a Socket Plug - Commonly referred to as the male end. Hansen Style Plug Hansen Style Plug Schrader Style Plug Schrader Style Plug Male Threads Female Threads Male Threads Female Threads Socket - Commonly referred to as the female end. A plug is a male-threaded closure for the end of a pipe or fitting — the opposite of a cap, which is female and slips over a pipe end. Used in threaded systems (galvanized, black iron, brass) to close off a tee outlet, terminate a pipe end, or seat into a cleanout fitting. A female thread fitting has the threads internally formed with a threaded tool called a tap. A male thread fitting has the threads externally formed with a threaded tool called a die. If the diameters increase for a male end or decrease for a female end, the thread is tapered. If all the diameters are the same, the thread is straight (parallel). Step 2: Measure the thread diameter. Use a caliper to measure the nominal male or female thread diameter from crest-to-crest (Fig. 2). Measure the fourth or fifth full thread. A pipe union has three parts; A male end, A nut, and a female end. The female end has threads on the inside whereas threads are outside on the male end part. The nut provides the necessary pressure and seals the joint. Fig. 2 represents typical pipe unions used in the pipe fitting industry. A threaded cap, also called a end cap, is used to close off and seal the end of a pipe or male threaded fitting. Threaded pipe caps are commonly used to close off male threaded ends to prevent contaminants from entering. They are used to create a tight seal that prevents leakage and stops the flow. Male thread: The threaded portion of a pipe, fitting or component that has external threads designed to screw into a corresponding female-threaded opening or fitting, creating a secure and sealed connection when twisted together. Male PVC fittings have external threads that screw into female fittings, which have internal threads. Think of it this way: male threads wrap around the outside, while female threads hide inside—they're designed to interlock perfectly.