Here's a very simple and clean DIY counterweight solution to add onto your 15mm Video Rigs. This tip comes from Jason and he shows us how a Balance Weight typically used on telescopes will clamp nicely to any 15mm Rail. [Thanks Jason]. He's using a Meade 1422 counterweight, but i'm guessing there are other versions that may work as well. Check out the products via eBay (click here).
Telescope Counter Balance Weight
There are also other versions of Telescope Counter Balance weights available via Amazon (found here)
Telescope Counter Balance Weights