3/8" Pex Crimp Tool, For Use With 3/8" Pex Copper Crimp Rings, For The Crimp Tool To Work Correctly It Must Evenly Compress The Copper Crimp Ring So That The Pex Pipe Is Evenly Forced Between The Ribs Of The Fitting, If The Ring Is Not Evenly Compressed, The Joint Could Leak, Using The Crimping Gauge, Go/No-Go Gauge, Helps Ensure A Quality Joint.