To Quote the Professor on Gilligan's Island, "If You Want Something Done Right, Do It Yourself."

The spider and diagonal holder I bought was inexpensive, and for good reason.  It was supposed to be for a 4.5" OD tube.  It was closer to 5", because one of the legs was substantially longer than the other two.  The diagonal holder was made of some unrecognized black plastic, likely nylon.  Its design was essentially identical to my aluminum diagonal.  I could probably have modified to meet my needs, but much of that time and frustration can be used to finish machining my design which is quite similar, although easier to make.  Why pay for sloppy work?