Made for the Zeiss 6x30 binoculars, but it looks like it could be used with several different eyepieces that have a 24.7mm diameter barrel. It has a set screw hole that keeps the scale from sliding down the barrel when focusing. Scale measures +/- 5 diopters. Top part is threaded to attach to the eyepiece focusing mechanism. There is also a split in the metal just in case your barrel is a bit larger. Unused.
