It's quite reasonable that the new Lubitel 166+ also has a "Universal" in its Name. Besides medium format, it also supports 35mm film and exposes the sprocket holes as well. Although some small black lines remain on the left and on the right, it's very easy to get rid of this imperfection.
When I’ve shot my first 35mm roll using the Lubitel, I sticked to the manual. Soon, I found out that the mask says “56 × 33mm”, but 35mm film is, well, 35mm and not 33mm wide.
It’s a pity that 2 millimeters remain unexposed, so i started the experiment with a Klick Max 200. I spared the sprocket mask. And it was a huge success.
From now on, I’ve never used the mask again, and loaded the film without the mask. I’ve never had any problems.
Apparently, the mask supports the film and holds it in place, but still, the 6th golden rule applies: Don’t think.