Resembling a bit guard is a bit burr (sometimes burr bit, also bubble cheeker in Australia), which has teeth laid against the horse's cheek. The burr bit was for a time widely used on coach horses in New York City, until the use was stopped in part through the efforts of Henry Bergh circa 1879.1 Bubble cheekers are approved for use in thoroughbred racing in Australia.2
Wood, John George (1885) Horse and Man: Their Mutual Dependence and Duties, Longmans, Green, 339 pages, page 221. ↩
Dion Villella. "Register of Nationally Approved Gear" (PDF). Racing Victoria Limited. Retrieved 2010-12-03. http://www.racingvictoria.net.au/asset/cms/Stewards%20Notifications%20PDF/128312%20RVL%20Gear%20Register%20Book.pdf ↩