1¼" Newtonian OCS (Optical Corrector System) in a plastic bolt case.
The OCS is a modular system that allows high and low power
configurations for newtonian telescopes using a Denkmeier binoviewer. For low power, unscrew the hollow nose piece from the binoviewer and thread on the 1¼" OCS. For high power use the hollow nose piece in place of Part O of the OCS.
Denkemeier list is $179, asking $134.