The advantage of Select-A-Vent is that you don’t have to commit to a vent size but can play around and find the size that you like best. There is the following info that I posted out of Harvey Dillon’s 2012 Hearing Aid book - which you’ve seen before. Dillon says there are effectively only 2 or 3 actual venting sizes attainable with Select-A-Vent because, for example, it’s hard to achieve total occlusion due to leakage around the mold so, for example, he says that no vent will basically be about the same as a 0.5 to 1 mm vent, etc., (might be described in more detail in some other previous post of mine).