Next time you visit a DIY store or builder, stop by the plumbing section to see the variety of small plumbing accessories available. Brass, copper, plastic, chrome - all in a chaotic arrangement of different sizes. But what do they do and how do they work?

The common name for these products is brass fittings. The term refers to their use with copper pipes (or alternatives such as plastic) for hot and cold water supply or central heating. Copper fittings do come in many different shapes and sizes, but they are generally grouped into four groups. These groups are derived from the actual method used when the accessories are put into service.

The first group is called welding ring accessories. Weld ring fittings (sometimes called Yorkshire fittings) are made of copper or brass. The fitting itself contains a small ring of cooled solder around the inner circumference of the fitting. When the copper pipe is pushed into the joint and flux (cleaning and activation paste) is applied at high temperature, the solder melts and flows around the joint, cooling and solidifying again once the heat source is removed, forming a strong joint.

The second type of fittings are called end-feed fittings. These fittings are almost identical to solder ring fittings, except that they do not contain a complete ring of solder - when using end feed fittings, the solder is supplied by the plumber from a reel or solder rod. When the pipe/fitting joint is at the correct temperature, the plumber provides the tip of the pad or sticks to the joint. The intense heat melts the solder, which then "pulls" or "feeds" the solder around the joint by capillary action. When the heat is removed and the solder solidifies, the joint is formed again. These fittings are favored by plumbers because they are significantly less expensive than weld ring fittings and are just as effective when used correctly.

The third set of accessories is named after the compression. These are usually brass fittings using the mechanical pressure fitting method, sometimes called "nuts and olives". An olive is a thin strip of copper or brass, shaped like a wedding ring, that is mounted on a copper tube with a threaded nut that is then inserted into the fitting, with the internal threads on the nut being screwed to the external threads on the body of the fitting. When the nut is tightened, the olive is pressed onto the pipe and into the recess in the fitting, creating a secure and waterproof fitting. When using compression fittings, some plumbers tend to use a proprietary plumbing compound around the olives.

The last group of the latest accessories are called push-on accessories. Cleverly designed using internal gripping rings, they are combined with technically advanced flexible plastic tubing, supplied in coils or lengths. Insert a small metal or rigid plastic pipe reinforcement into the end hole of the pipe, ensuring that the pipe wall does not deform under pressure. Then insert the tube into the fitting until it reaches the integral stop inside the fitting, making sure the catch ring is in the correct position. The joint then reaches its full strength when pressurized by the water flowing through it.

Regardless of which of the four groups the fittings belong to, their dimensions are always referenced to the diameter of the copper pipe they are used to connect to. The most common sizes for domestic plumbing applications are 15mm, 22mm and 28mm.

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