They are Gepe rotary transfer magazines, that are used for easily and quickly transferring the full magazine of slides from a Kodak rotary magazine into these Gepe magazines for storage. So if you have Kodak rotary magazines and you need a quick and easy way to move slides in and out of these magazines (rather than moving slides out one-by-one and then inserting them all again) - you can place this magazine onto the top of the Kodak magazine, turn it over and all slides will transfer from the Kodak magazine to the Gepe storage magazine!
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