Another *very* satisfied RB4001 owner here. Robert was right on the money. These barndoors are very well built and are worth the price of admission if only for the ease with which they accept 7" Speedotron grids. No more wrestling with the nude 7" Elinchrom reflector.
While I was at it, I also ordered the AC8011 color filter set. It contains 7 filters (red, blue, green, orange, magenta, purple, yellow) mounted in cardboard frames. I would have preferred plastic frames but these will do the job. They're certainly a vast improvedment over taping gels to reflector rims.
One last note: I called Interfit USA today to ask about the INT207 barndoors for tungsten lights. They confirmed that they too are all metal construction.
Thanks again, Leo. Great find.