[cctalk] IBM RAMAC platter

Greetings! I recently stumbled across a early hard drive platter that appears, based on measurements, to be an original RAMAC platter.  Very little comes up in Google beyond basic measures (diameter of 24" and a head motion of 6".)   I'm curious if there was anything out there that had similar measurements.   I did find a photo on facebook but it clearly has different measurements. Platter is in poor condition (no oxide, nicks and dings, etc although still obviously a platter) but the owner is fascinated with possible origin. Steve