Collar days are designated days on which the collar forming part of the insignia of certain members of British orders of knighthood may be worn.
Collars are special large and elaborate ceremonial metal chains worn over the shoulders, hanging equally over the front and back, often tied with a bow at the shoulders, with a distinctive pendant attached to the front.
Collars are worn by Knights and Ladies Companion of the Order of the Garter, Knights and Ladies of the Order of the Thistle, and Knights and Dames Grand Cross of other orders.
The collar can be worn on specific collar days throughout the year.
Collar days, in accordance with instructions of the Central Chancery of the Orders of Knighthood, are:[1][2][3] Collars are also worn when the King opens or prorogues Parliament, and for a few other observances, including religious services of the various orders, and by those taking part in the ceremony of introduction of a peer in the House of Lords.