Hello As the schwinn expert on my block i m inclined to say it is for a prewar seat .The prewar seats have taller clamp compared to later years and if you try to put them on later model posts the part that pinches the seat pole tops out over the pole preventing the clamp to work as designed.
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The example shown - while not schwinn has enough area at top for clamp to Lock on to it furthermore, if it is same diameter as versions next to it would be happy to purchase it