Why are most Finger spools 3 inches in diameter? (7.5 cm = 2.95") Simple, in the early days when divers were making their own gear 3" diameter delrin bar stock was pretty easy to find. That lead 3" (or close to it) to become a defacto standard for finger spools.
3" is fine, but is it optimum?
Consider any spool. The last few turns of thread, or fishing line or kite string around the maximum OD of the spool are far longer than the last few turns at the core of the spool. Circumference = diameter * pi. Ever a new roll of paper towels seems to last pretty well for the first half and then the 2nd "half" disappears in a day or two?
Recognizing this phenomena I designed the DSS spools to have a larger OD, 3.3" vs 3.0 and a larger ID. The larger OD allows for more capacity and the larger center hole reduces the "reach in distance" (first finger to thumb) and provides room for big hands and cold water gloves.
The with each turn being longer on a 3.3" spool vs a 3.0 DSS spools can be narrower than a 3.0 and do not have to filled to the point the clip holes are covered to reach their rated capacity.
Tobin
