Designed to help prevent overflowing from a roof valley in heavy rainwater conditions; a common problem with conventional inside box miters and inside miter strips. A SUPERIOR WATER OVERFLOW SOLUTION – Inside mitres are susceptible to heavy rainwater flow from roof valleys. The Extreme Miter’s Inside Gutter Corner’s enlarged catch basin helps direct water away from the front edge and channels it through the gutter troughs to prevent overflowing. A QUICK, SECURE INSTALLATION