The flowlights give flowtoys a good heft, but if you like a heavy feel to your tools, you can add flowmass to the ends of your flowtoy - where they count - to give them more momentum. Each flow mass adds 30g to you props.
Double mass is two sets of regular flowmass and is recommended if you are turning your standard flowtoys glow staff into a contact staff.
Applying a small amount of Vaseline/chap stick to the insides of the mass can help to install them on tubes. Do NOT do this if you are installing on crystal cases as the mass could then fly off while spinning.
The mass can be installed onto crystal cases, all flowpoi, staffs and other tubing based flowtoys. You can remove them with water or rubbing alcohol.
They are sold singularly so you'd need 4 x flowmass to have double mass on your staff - two at each end.
Please note that flowmass do not fit on flowlights alone!