Polaroid 550 Film Holder Question

Recently purchased a used B&J 4X5 Orbit mono-rail camera. While looking into po laroid backs on their website the description for the 550 film holder stated it works on all "locking rib" backs.

Can someone define "locking rib" back. Not being well versed in LF, my camera h as a film back that rotates, a lever for moving the ground glass away from the b ack to allow for insertion of film holders. I heard/read about Graphlok & Graph lex and universal backs but have not visually seen them. Any assistance greatly appreciated.

P.S. I attempted to do a search for the info, however, there is no search forma t as there is on Philip's other web pages.

They mean the Graflok or "International" back. For some pictures and discussion, go to the Graflex web site: www.graflex.org