About to order the modified vacextender v4 - which size to choose?

Looking at autoextender. Com I’m not sure what size to pick. I’m average in size, and the site offers size small, medium and large. While a know what mm I need on the rods to connect the vacuum system to my extender, I don’t understand what the small-medium and large option represent, the vacuum cylinder? If so, what to choose? The site doesn’t bother to even mention anything of this. Thanks

If you look at the vac ads purchase page there’s a dropdown menu with the sizes in inches.

Also on the vacads 4 info page.

Small 1.4”

Medium 1.6”

Large 1.8”

I believe the sizes are the inside diameter of the base of cap that fits onto the glans. When there were only two sizes (large and small), Monkeybar recommended the large size for most guys.

I have to bump this thread as I still haven’t order the system but are doing it now.

I’m a bit confused about the size chart posted above. Do I measure in complete flaccid state, with no blood forced in to the glans? From the two widest points on the glans? My flaccid-glans size can change pretty much just by doing some very few light kegels. Obviously its better to get an cylinder which is a little bit too big vs too small? Too little space in the vacuum cylinder would cut off circulation and while too big would create fluid buildup, it can be controlled with tape? I would appreciate any advice.