The five articles of faith given at the founding of the Khalsa in 1699 are kesh, uncut hair; kangha, the comb; kara, the steel bracelet; kachhera, the prescribed undergarment; and kirpan, the sword. Four of them are worn. One of them is used.
The kanga is a small comb, traditionally of wood, kept in the hair itself, tucked into the joora, the topknot, under the turban. The Sikh code of conduct directs that the hair be combed with it twice a day and the comb replaced in the hair afterwards, and that is the whole of the instruction. It is not an ornament, not a token and not a miniature; it is a comb of the size and shape that will actually comb hair that has never been cut.
Its necessity follows directly from the first of the five. Hair that is never cut has to be washed, dried, combed out and bound, every day, for a lifetime, and that is a real discipline requiring a real tool. The comb is therefore the article that makes the article above it livable, which is why a reference list can make it look like the least significant of the five when it is the one doing the work.
The object itself is deliberately modest. It is a few centimetres across, traditionally turned or carved from wood, and now also made in plastic, horn, ivory substitutes and steel, sometimes matched to the kara. Many people keep two, a working comb in the hair and a spare, and a broken one is simply replaced. Nothing about its material is prescribed, and no version of it is treated as more valid than another, which sets it apart from the kara and the kirpan, where the metal itself carries meaning.