Need Help IDing Odd-Size Card File Cabinet

Just scored a new card file cabinet on Craigslist, and it's an odd one. The sizes are unusual -- not built for the usual 3x5 or 4x6 cards. I have two 3x5 card file cabinets, and a friend of mine has some 4x6 cabinets. This one is definitely not either of those.

I have a hunch (a guess, really) as to what it might have been for, but I want to query the Card Cabinet Aficionados of Garage Journal to see if anyone recognizes it or has seen one before.

I'm guessing aperature cards.
If I recall Microfiche were taller and not as long.

ducksface said:

Punch cards.
Standard IBM size. Just over 3 by just under 7,5
(from memories of when I was five years old)

Click to expand...

That was my guess. Seems like the right dimensions for punch cards. Never seen a punch card file cabinet before, but I guess they had to store them somewhere.

Leaflessshadetree said:

I'm guessing aperature cards.
If I recall Microfiche were taller and not as long.

Click to expand...

I had never heard of aperture cards. Fascinating hybrid tech!

Punch cards.
Used to operate a 4341

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Sounds like we have a consensus. Thanks, all!