You are buying a 1"FTB X 3/4" Barb Pump Union with O-ring that matches the Union. The Union receives a 3/4" Inside Diameter Hose which measures about 1" on the outside and then Screws to a 1" Wetend (Pump) Threaded Part on the other side the threads will measure approximately 1 7/8" outside to outside. It will receive a 3/4" hose over the barb and screw to a 1" Wet End fitting. Don't be confused we also offer other 1" pump unions a well as Pump unions that are 1 1/2" Slip X 1 1/2" Pump Wet End or 2" Slip X 2" Pump Wetend or a 2" Slip X 2 1/2" pump Wet End. If your plumbing hose is 3/4" Inside and your Pump Wetend Thread is 1" Meaning it measures 1 7/8" Across then this part is correct. Generally This fits a Waterway Tiny Might pump both suction and pressure. Shipping in The United States is Free. I Ship International Through the Global Shipping Program Only!! Please Choose with Care as We Do Not Accept Returns.We have done a lot of extra work with videos and pictures to prevent you from choosing the wrong part..