O4 (US desig) Sqn Ldr / Lt Cdr / Major
OF-4 (NATO desig) is Wg Cdr / Cdr / Lt Col
OF-5 is a Gp Capt / Capt / Colonel
An SO1 is a Staff Officer of Wg Cdr level (SO2 is Sqn Ldr etc) which is often incorrectly used to refer to a rank across the board (i.e. flying or field job), rather than a rank in a STAFF post (i.e. HQ).
It's all rather tiresome frankly, as is this banal thread, started by a complete troll.