The suction cup is the most important part of your tools as it controls the pressure. The pressure that injects the resin comes from the suction cup(s). Do not ignore this very important part of your repair tool. The wrong cup can ruin your repairs. This custom made cup is two inches and has the perfect durometer so you do not spread damage or cause flowering. Cups should be changed every sixmonths to a year and you should change both cups on tools with two cups at the same time.