i understand it is a kewl entrance, from another thread
i bought one and propmtly rolled the queen on the bottom of the frame as the 6mm-8mm gap under my frames was insuffieceint to take a frame of bees shook into the bottom and the Q...so ihave addeed a 21mm eKe to give the same Beespace under frames as in the original 1970 BS national British Standard =28mm...7/8 inch plus 1/4 inch
Thanks for that MM, I mount the mesh on three batons to the sides and rear and the top of the front wall of the main floor area. The mesh is some 20mm below the top bearing surfaces.
I like a sufficiency of space below the frames to give both myself and the bees a bit of a margin and elbow space to give them somewhere to go if frames are put in on top of them. Once they start taking up building on the bottoms of the frames, it's usually a sign that they are looking for additional space and time to provide it with additional box space in the form of a super or brood box if that's the way you might wish to go.
Having asked the question, I came across the other post mentioning Kewl also. Sod's law in action of course.