This page is credited in full to Dave Cushman who created it. His voice is expressed in black colour text and any additions or comments in blue belong to myself. Credit: Dave Cushman’s website.
The item depicted in this drawing is as manufactured by… APEX Enterprises and is similar to those manufactured today by E.H. Thorne in UK.
The main panel is 6 mm or 9 mm plywood, the upper rim is 9 mm x 22 mm material and the underside rim is 63 mm. (see notes on clearer boards page about alternative 22 mm deep rim dimensions) I would use a 22 mm deep rim if I were to make any more.
The red cone escapes are fitted from underneath into 22 mm diameter holes.
I do have one of these units in my kit. I can say that it works, but I cannot give any relative effectiveness to the other types as my original data is “lost” and I can’t remember how good it was when I actually tested it. I can say that it was not outstanding in performance otherwise I would have adopted it for more widespread use.