How do you play f flat on clarinet?

To play F♭ on the clarinet, you must cover the upper joint register key (also called the trill key) and the first five holes, but you must leave hole 6 uncovered. For the lower joint, you must cover holes 6, 7, and 8, but leave holes 9 (and 10, if you have a low E♭ key) uncovered.