Twilleys, 8082/0400, 4.00mm Aluminium Needle. 30cm long.

 Knitting Needles
There are three main types of knitting needles, single-pointed needles with knobs at one end which are used in pairs to knit flat pieces; double-pointed needles, used in sets of 4 or 5 to knit small seamless items (such as socks etc.), or more frequently for neckbands or armbands, and circular knitting needles, which are used for knitting seamless sweaters and also where a large number of stitches is involved such as a rug or shawl. Single and double-pointed needles can be made of plastic, wood, bamboo, steel or alloy and range in size from 2 mm to 17 mm in diameter and 17.5cm to 35 cm in length.
Most knitting patterns nowadays recommend a metric size needle. If you are using old needles, which have only got the old numerical size on them, it would be best to check the size of the needles with a needle gauge (see below). Circular needles, consisting of two needlepoints joined by a flexible length of plastic, are usually made of nylon or alloy. The flexible plastic cord varies in length. Use the shorter lengths for knitting sleeves in the round, neckbands, etc. and the longer lengths for larger pieces such as sweaters and skirts.
Always use a needle of a length sufficient to hold the stitches comfortably. A crowded needle is difficult to use but too long a needle is hard to manage unless you like to knit with one end tucked under your arm.