Oh, as to the original question - the correct answer (for ME anyway :=) is either 7, or 12, or NONE - All depends on how you count 'em (and whether your loader can handle over 2 TONS or not)...
All tubes are 2.030" ID, 1/4" wall - note the cutaways on top edges - some of my "tinker toys" weigh in around 100 lbs - it's much easier to NOT have to line up perfectly while holding ALL the weight...
The center part of the bucket got a piece of 10" heavy channel bridge, water tight welded 100%, with a receiver centered on top. ALL receivers (EXCEPT the two that line up with loader arms) can be used front, back, or both - the loader arm mounts interfere with rear clearance on those two (hence "12" and not "14" receivers.
So far, I have 3 pairs of extensions made at 30", 48" and 72" - all inserts/adapters are same material or males are 2" tubing, still 1/4" wall. I've made inserts for 45 or 90 degrees, Tees, male/male, female/female, etc - also various other attachments depending on need. I haven't needed to add any "options" for awhile, buy will if/when the need arises that can't be met with current "toys"...