Throughout much of the 1950s and 1960s, the most popular style of windows used on travel trailers was the Hehr Standard model.  Airstream used them routinely from 1952-1958.  These awning-style windows are characterized by square corners, but a round-corner look.  The glass is held in with aluminum brackets screwed in place from behind using 8-32" slotted truss head machine screws and 8-32" stamped steel tension nuts.  The original stamped nuts are self-locking and very hard to find.

To replace missing or rusty screws and nuts, use this kit of 100 screws and 100 nuts.  

Zinc plated steel.