There is no absolute standard for 18x24 holders but 3 major types that I know of.
- 2 full thin slots which fit into (somewhat ugly) brass strips on the back.
- Brass corner strips which fit into concealed corner slots.
- Wide center groves at corners on the film holder which fit into wood ridges in the back.
Type 1 holders are never the book type (mostly French cameras - or made for the French market).
Most of the other types are Book holders.
The design of all types is such that - within the type - it is quite realistic to modify the holders' width to fit the back.
Bookmarks