http://www.pacificrimcamera.com/pp/graflex/backs.htm
describes and covers most of the accessories associated with the type of backs.
Graflex: holders are 1/8 to 3/16 inch wider than standard film holders, the same length, film plane at a different depth than standard film holders; have slots down their sides and a grove close to the darkslide end that mates with the back frame edge to form the light trap. Graflex has a straight bar slider top and fixed bar bottom for most the production years; late production models have flat slide bars top and bottom. Graflex backs are the only back supplied by the factory for their SLR's and were an option on Speed Graphic cameras up to the early 1950's.
Graphic: common spring back found on many makes of cameras; takes standard two sided film holders. A Grafmatic may not fit on some cameras and will expand the springs to their limit on others.
Graflok, aka International Back: takes all types of standard film holders and accessories; has a removable focus panel; slide bars top and bottom are angled inward and used to lock accessories in place.
Slide bars on Graflex and Graflok backs were made sidling left to right to lock, most common, and right to left to lock, less common.