This part is a 3/4" Barb Adapter x 3/4" Slip / 1" Street.
The Glue Side glues inside a 1" Fitting (like a coupler) and the inside would fit a 3/4" connection.
Barb Adapter 3/4" Barb x 1/2" Spigot , The Glue Side glues inside a 1/2" Fitting which would measure 3/4" and a 3/4" ID tube would be glued over the barb.
You are Purchasing (1) 3/4" X 1" Barbed Coupler that fits 1" OD , 3/4" ID Clear Hose on one side and 1 1/4" OD , 1" ID on the other side. These are used for connecting Clear Hoses together in Hot...
Barb Adapter 3/8" Barb x 1/2" Spigot , The Glue Side glues inside a 1/2" Fitting which would measure 3/4" and a 3/8" ID tube would be glued over the barb.