Both the pocket and the file have to be A3, since an oversize protector in a standard binder simply folds over. Check the punch pattern matches the mechanism as well as the size. Gauge follows handling, because a thin pocket on a plan consulted daily curls at the opening within weeks. See sheet protectors, A3 dividers and binders.

A3 sheet protectors arranged on an office desk with a large plan binder, architectural drawings and filing supplies.
A3 Sheet Protectors for Documents and Artwork

Shop A3 sheet protectors for plans, posters, artwork, charts and larger document storage in offices and schools.