For full body width Diaphragms, take a look at The Coach Yard.
Diaphragms, or connecting corridors, were used on passenger trains consisting of central-corridor coaches. They allowed people to safely walk from coach to coach, and if the engine was designed to allow it, from the coaches to the engine.
Diaphragms are/were used between any type of pax cars (e.g. lounge, dinner, sleeper, coach, baggage, RPO) not just between coaches. If the cars & locomotives were on the same level then trainman could walk between engine & cars thru the diaphragms. It doesn't work anymore between modern locomotives & bi-level cars.