The term 'British Automobile Part' can be broken down into three crossword solutions: JAG (3 letters), STEN (4 letters), and ROLLS (5 letters). JAG is an abbreviation for Jaguar, a British luxury car manufacturer founded in 1922. STEN is an abbreviation for the Sten submachine gun, a British submachine gun used during World War II. ROLLS is an abbreviation for Rolls-Royce, a British luxury car manufacturer founded in 1904. All three of these abbreviations refer to parts of British automobiles.