Pattresses contain devices for input (switches) and output (sockets and fixtures), with transfer managed by junction boxes. A pattress may be made of metal or plastic. In the United Kingdom, surface-mounted boxes in particular are often made from urea-formaldehyde resin or alternatively PVC and usually white. Wall boxes are commonly made of thin galvanised metal. A pattress box is made to standard dimensions and may contain embedded bushings (in standard positions) for the attachment of wiring devices (switches and sockets). Internal pattress boxes themselves do not include the corresponding faceplates, since the devices to be contained in the box specify the required faceplate. External pattress boxes may offer include corresponding faceplates, limiting the devices to be contained in the box.

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  External pattress boxes:
  Power and Data Sockets

Although cables may be joined inside pattress boxes, due simply to their presence at convenient points in the wiring, their main purpose is to accommodate switches and sockets. They allow switches and sockets to be recessed into the wall for a better appearance. Enclosures primarily for joining wires are called junction boxes.

New work boxes are designed to be installed in a new installation. They are typically designed with nail or screw holes to attach directly to wall studs.

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  New work pattress box.
  Nails attach box to side of stud.
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  New work pattress box.
  Nails attach box to face of stud
  via metal bracket.

Old work boxes are designed to attach to already-installed wall material (usually drywall). The boxes will almost always have two or more parsellas (from Latin: "small wing or part). The parsellas flip out when the box screws are screwed, securing the box to the wall with the help of the four or more tabs on the front of the box.

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  German round old work pattress box
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  German round old work pattress box
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  round old work pattress box

In some countries, for instance in Germany, wall boxes for electrical fittings generally are not actual rectangular boxes at all but standard-sized round recessed containers. This has the advantage that the corresponding round holes can be simply drilled out with a hole saw rather than needing the cutting-out of a rectangular cavity to accommodate the wall box. Even with those round-hole systems, the faceplates that cover them are mostly rectangular however.

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  UK-pattern single (1 gang) white plastic surface pattress box
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  UK-pattern double (2 gang) metal wall box for sub-surface use

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  US-style new work wall box with room for three light switches. To be nailed sideways to a wooden beam.
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  US-style new work wall box (blue) behind two light switches. Not shown: the corresponding faceplate.

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  ψ-way light switch with fitting box
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  TEM fitting boxes

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  round wall box
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  Dual light switches in square wall box
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  Three light switches in square wall box

• Wall anchor plates are also known as pattress plates.
• Junction box, an enclosure housing electrical connections
• Electrical wiring in the United Kingdom
• Electrical wiring in North America
• Light switch
• AC power plugs and sockets

• DIY Wiki Pattress page – more information on (British) pattresses and terminology