Eight frame equipment varies in size from manufacturer to manufacturer. According to my cut sheet, an eight frame telescoping cover should measure 15-3/4" wide by 22" long. Yours is just slightly larger in both directions which may be due to measuring across the metal top and not the side rails themselves or because it is a different manufacturer than the one I copied.
13-3/4" wide is the normal, but Mann Lake makes their 8 frame boxes 14" wide. The 14" width leaves enough open space inside that you can almost fit another frame. The ML queen excluders will over hang 13-3/4. I use 13-3/4, the overhang isn't a big deal but I live in a dry climate, if I was somewhere that rained a lot I'd either want a QE that fit or I'm make the box fit the QE.
A forum community dedicated to beekeeping, bee owners and enthusiasts. Come join the discussion about breeding, honey production, health, behavior, hives, housing, adopting, care, classifieds, and more!