(Obsolete) Caliburn Solid Buttplate

Do not print, use CaptainSlug's current captive nut version instead.

This is the Caliburn's back stock part (ButtplateTPU.stl) that comes with the fileset, barely modified to be solid instead. This was done just hours before CaptainSlug added solid variants of the buttplate the other week, so I would recommend printing that instead.