Your informaition and pictures were most helpful. I have been wondering for some time how well these clamps work and will pick one up now. (I have been using different size flat head nails hooked into my vise jaws but its not always as secure.
I use many different types of tubes (Mostly imported from UK) but unless I fishing fast or deep waters for Steelhead I have found the 'Q tips' type cotton swabs with the plastic, not carboard, shafts work really well and you can buy a box of 300 for around $3.00.
I simply cut off the cotton ends to whatever length of tube I need.
If I am making up articulated tube flies, which I use mostly for sea runs, I slip a suitable on coloured bead between the tube and the hook to get max movement from the tail section.
One again appreciate your posting and pics.