The earlier versions had 2 1/2” thick walls.
Of these three models, only the F-500 previously came standard with a mercury relay, which controls the cycling of the heating elements. Now the F-130 and F-240 also ship with a mercury relay instead of mechanical relays.
The F-500 has had a slide-out mandrel holder for two years. Paragon just added that to the F-130 and F-240. The mandrel holder (also called a point rest) on these kilns can be adjusted horizontally and vertically without tools. The holder slides inside steel tubes, which are hidden in the base of the kiln.
Previously the F-130 and F-240 could be special-ordered with sidewall elements; they came standard with the F-500. Now these models all have sidewall elements instead of top elements. The elements heat from the sides and back in dropped, recessed wall grooves. But if you prefer, you can still order these kilns with elements in the top instead of the walls; the price of the kiln is the same.