Interesting.
I noticed a while back that there was a Microseiki base weight on offer, that screwed in under the arm board - rather than the usual nut, this was a very chunky 5-6cm deep heavy weight, that screwed in to 'stabilise' the armbase (into which the arm is secured by two grub screws). What would be the physics of that? Any damping effect from adding mass there rather than on top?
My Ikeda armbase is exactly the same screw thread as the FR64S, also I guess the size means it could be done up quite tightly just by hand pressure. The Ortofon works a bit differently as the base is a sliding SME-type into a collar (the base secured to the armboard by four bolts, SME-style) so no potential for similar really. Neither are really amenable to adding mass from above ... the Ikeda has a round top over the bearing, so a bit harder to put a weight on top while the Ortofon has quite a narrow retaining ring for the bearing assembly.
http://i1181.photobucket.com/albums/...psszbvvalw.jpg