I'm trying to find out if there are any differences between the 35 & 40 MCONS besides their diameters?(62mm,55mm respectively) I am using an UZI. I'm asking because I would like to switch between just using the macro, and using the macro in conjunction with a tcon17? I found some instructions on how to attach a mcon35 to the front of the tcon, but I'm not sure if I would have problems with stepping down from 77mm-55mm. On the other hand, using the mcon 35, I would have to step from 55mm-62mm. Am I correct in assuming that is is always ok to step up, but not as much to step down? Has anyone here ever attached anything to the front of their tcon17?