Comes with original Televue box, and end caps. It looks like a very short 2" Barlow, it is intended to go into a 2" Barlow, and then the 2" Panoptic eyepiece goes into it.
From Televue: To increase the power while retaining eye-relief, add the 2x Big Barlow and matching interface lens. The interface pulls the pupil back to the ideal eye-point, preventing vignetting and further optimizing edge correction to "Nagler" levels. When using the 2x Big Barlow, we consider the interface lens essential with the 35mm and 27mm, helpful with the 22mm and unnecessary with the 19 & 15mm.