Though they seem to be light, AirFit rings are commonly used in pen modding to add great momentum to your pen for Pen Spinning .
They also make your pen mod look prettier.
Prices are marked in US Dollars, and they are a reference prices, so it doesn't matter, which currency you use, it will be automatically converted to Rubles anyway.
Products are custom made and can slightly differ from pictures.
How to filter pen mods on Pen Stock