This set of three adhesive-backed shims fills the gap between the ring fin and the booster stage bottle. Just peel-and-stick. They should be spaced evenly
around the circumference of the booster bottle, under the resting place of the upper stage's ring fin. They are made of very light closed-cell foam.
Useful for making water rockets, pop bottle rockets, water bottle rockets, pop bottle water rockets, water pump rockets, soda bottle rockets and bicycle pump rockets.