just get a 22mm compression straight and an imperial olive, just in case, here they are called green rings, as they had green paint on to signify that they were 3/4, only cost pennies , so if you dont need it you havent wasted any money, if it is 22mm you wont be able to push the 3/4 olive on, if it is 3/4 the 22mm olive will be too slack