Each tin contains 1oz (28.4g) of a squishy black substance known as Nibbler Poop. Primarily used as rocket fuel, it is also quite useful for balancing hand wheels. 

This dense black substance is made from pure dark matter, making it one of the densest substances known to man. On Planet Earth we call it Tungsten Putty, but in actual fact it is made from the poop of Nibblonians, who are a species of cute dog-like creatures from the Planet Eternium. See the documentary 'Futurama' for a more detailed explanation of it's origins. 

 It is very dense, sticky and non-toxic, and is great for balancing your wheels to the point of perfection. In order to counterbalance the various handles you will need 1 tin per 2-Button Handle, 1.5 tins for each Plain Handle, and 2 tins per wheel if you wish to use the Handle Stubs on their own. Break off a small amount of putty and stick it to the back of the wheel until it is balanced. Then squish the right amount of putty into the counterbalance slots at the back once you are happy. You can also pack the right amount into the hollow cavity inside the Plain Handles if you want them to match the weight of the 2-Button Handles, making it quicker to switch between them.