Definitely not for the Geiss or Hakosyn. But it's certainly looks like it's designed to prevent anything that's clamped-on from slipping or rotating.
I considered it might've been for a linked light-meter, like the MC for the Leica M cameras. But that would be kinda strange as you can't lift up the dial to set the wanted speed.
Rick - In Tabulas Argenteas Refero
Loaded with film: Leica IIIc and a Graphic 23 roll film holder
Latest Toys: Agfa Billy Record, K.W. Etui, unknown 9x12 folder.