>On this particular model, the center column has a triangular >shaped plastic piece on the bottom of the column with a >mounting screw. can someone please advise what this is used >for....? > >1) mount camera upside down? >2) used to mount a head when one doesn't want to use the >center column (ie, remove the center column, remove plastic >piece and insert into the hole at top of tripod? >3) other? > >thanks!
If it's the same as on the 3021, the plastic triangular-shaped plug is just a spacer for the legs to butt against when they're folded. It's a loose fit in the end of the column and not nearly solid enough to mount a camera on. The 3/8" threaded stud may be meant for attaching a stabilising hook or other accessory. On the 3021 the plug can be removed by pressing in a sprung retaining pin, which allows the column to be removed and/or reversed, so your ball head ends up underneath if you want.
PS - If yours has a screw instead of the sprung pin, you may need to carry a screwdriver, but I think the purpose is the same.