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.
Have you tried calling VPI Dodgealum? They may be able to give you the exact measurements fairly quickly. Just a thought. Good luck with the XX2MkII when it arrives.
Do you know that there is a movable weight on the inside of the arm which is controlled by an Allen wrench adjustment at the very back of VPI arms? What I do is set the weight for the highest approximate setting. To lighten the arm incrementally, insert the proper Allen wrench into the back of the arm and unscrew the weight little by little until you have the downward force you need....very easy.

The early Scouts do not have the threaded insert. Mine is one of those. Thanks though.
On my Scout, it is exactly 12.61mm, corresponding to 0.496457".
Romaxim--you rock. Thanks.
The O-rings that will work for you are as follows:

-014 1/16" thick (0.489" I.D.)
-112 3/32" thick (0.487" I.D.)
-206 1/8" thick (0.484" I.D.)
-310 3/16" thick (0.475" I.D.)***

Those are very close to the O.D.(within 0.010", except***) of the endstub so you they should slide easily. If you want a tighter fit, just subtract 1 from each "dash number" I gave you.
Worked beautifully--thanks. Now I can adjust the tracking force in minor increments without screwing up the azmuth.