A shive is a wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

en or plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 fitting used in ale

Cask ale

Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer which is conditioned and served from a cask without additional nitrogen or carbon dioxide pressure...

 casks. It is found on the curved side of the cask, arranged so that when the cask is on its side and the keystone

Keystone (cask)

A keystone is a small wooden or plastic fitting used in ale casks.For some years wooden casks have been effectively obsolete, with the majority now being aluminium or stainless steel, and a few sturdy plastic ones beginning to appear. Nevertheless, the standard tap is still designed to be hammered...

 is at the lowest part of the rim, the shive will be the highest point of the cask.

The hole in that part of the cask is used for two purposes. Firstly, it is used for cleaning out and then refilling the cask, which requires a large hole. Once the cask arrives at its destination, the hole is used to control the amount of carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 present in the container, which requires a small hole. The shive is effectively an adaptor that reconciles these conflicting requirements. It is a wooden disk, larger than a keystone, that fits in the hole in the cask and has a smaller hole in its centre.

For washing and filling, the old shive is removed using a chisel or a special tool, revealing a hole around 3 inch

Inch

An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...

es (7.5 cm

Centimetre

A centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the SI base unit of length. Centi is the SI prefix for a factor of . Hence a centimetre can be written as or — meaning or respectively...

) across. Once the cask has been filled and fined

Finings

FiningsThe term is a mass noun rather than a plural. are substances that are usually added at or near the completion of the processing of brewing wine, beer and various nonalcoholic juice beverages. Their purpose is for removal of organic compounds; to either improve clarity or adjust flavor/aroma...

, a new shive is hammer

Hammer

A hammer is a tool meant to deliver an impact to an object. The most common uses are for driving nails, fitting parts, forging metal and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure. The usual features are a handle and a head,...

ed into place. The hole in the centre of the shive will be sealed with a small wooden or plastic peg. The cask is then transported to the pub.

Some time before the beer is to be served (two or three days is common; especially strong beers may require more) the cask is opened or "vented". This entails breaking the seal in the middle of the shive by punching it through into the cask with a mallet

Mallet

A mallet is a kind of hammer, usually of rubber,or sometimes wood smaller than a maul or beetle and usually with a relatively large head.-Tools:Tool mallets come in different types, the most common of which are:...

 and some kind of tool. A spile

Spile

A spile is a small wooden peg used to control the flow of air into, and carbon dioxide out of, a cask of ale.Cask ale is served without externally-supplied carbon dioxide or nitrogen...

 is then placed in the hole to regulate the gas flow. If the beer is particularly "lively" (common in warm weather and with specific beers) the contents may spray out when the cask is vented.

During use, the hole in the centre of the shive can also be used (with the spile removed) to insert a marked dipstick

Dipstick

A dipstick is one of several measurement devices.Some dipsticks are dipped into a liquid to perform a chemical test or to provide a measure of quantity of the liquid....

in order to measure the quantity of beer remaining.

As with keystones, it is considered good form to close up the hole in the shive when returning empty casks, both to prevent spillage and to reduce bacterial and fungal contamination.