VPI Scout Rear Stub Measurement

I have a plan and I need some help. Can anyone tell me the precise diameter of the end stub (where the counterweight slides over the rear of the arm tube) of a VPI JMW9 tonearm? I do not have a veneer or micrometer to get a really accurate measurement and I'm hoping someone out there has the means to take a proper measurement.

I am going to be setting up a new cartridge this weekend and I want to try out a solution to a problem I've noticed when setting up the tracking force with the Scout--the slightest adjustment of the counterweight forward or aft makes too large a difference in the tracking force applied. My plan is to buy a series of O-Rings of different thicknesses (i.e. weights) and slide one (or more) over the rear of the arm tube and then slide them forward or aft to make incremental changes to the tracking force. This, I think, will give me a fine adjustment capability that the arm currently lacks and allow me to set the azmouth (sp?) once via the large counterweight and then fiddle with the tracking force without messing up this parameter.

Can anyone help me with a precise measurement? I want to get O-Rings with the proper ID so that I get a snug fit over the rear stub--too tight and they won't go on or slide easily enough, too loose and they will flop around and potentially change the tracking force.

Thanks. I'll share out the results of my "fix" so others can profit if it works.