Knitting needles, or knitting pins, as they are called in British English, come in three basic shapes: Single-point needles, double-point needles, and circular needles. In addition, there are two forms of cable stitch needles which are universally referred to as needles. Knitting needles are made with a variety of materials and available in a number of sizes. The needles required for a particular pattern are indicated in the instructions.
Single-point Needles. Single-point needles are the most common knitting needles, used for making flat knit pieces in a wide variety of patterns. They consist of a long, pointed shaft, with a cap on which their size is usually indicated. These knitting needles are straight, rigid, and made of aluminum, steel, plastic, or various woods such as bamboo, rosewood, ebony, or birch. Most are cylindrical, but at least one company offers a “square” version, which it claims are useful for people with stiff hands.
Double-point or Double-Pointed Needles. Made of similar materials to single-point needles, double-point knitting needles are used in sets of at least four to create seamless circular items, like tube socks, sleeves, or mittens. They can also be used for flat items. The number of needles required depends on the circumference of the item being made. In knitting instructions, these needles are often indicated as “dp.”
Circular Needles. Made of flexible nylon “cord” with metal, plastic, or wooden tips, circular needles are used for seamless circular items that are too large to work comfortably on double-point needles. They can also be used for very large flat items, such as afghans. Because the circumference of the piece being knit must be at least 2 inches (5.08 cm) larger than the length of circular needles, this will determine when to choose each needle type.
Cable Stitch Needles. Cable stitch needles are the only knitting needles with a built-in bend, specially designed to keep the cable from slipping off. There are two designs. One looks like a small hill in the middle of a long highway and is sometimes called a straight cable stitch needle or a cable stitch holder. The other type looks like a double-point needle with one end curved under, and always seems to be called a cable stitch needle. Each of these comes in a larger and smaller size, sometimes referred to as bulky and regular. They also often come in packs of three, with a bulky and regular needle and one “holder.”
Sizing. When buying knitting needles, it is important to consider both the length and the diameter. There are two completely different schemes used to size US and British knitting needles. Length is given in inches or mm, and diameter in a sizing scheme that runs from 0–50 for US sizing (~.08-1 inch) and from 2.1–25.4 mm for British sizing. The same size needles –- whether single-point, double-point, or circular -- are available in a variety of lengths in both systems. Sizes above US 17 are sometimes called jiffy needles because the large diameter and resulting loose weave mean that the work progresses quickly.