This part is a Barb Adapter, 3/4" Barb x 1" Slip..
That means that it will accept 3/4" Inside Diameter Tubing on the barbed side and a 1" Pipe or Fitting that would measure about 1 1/4" Outside...
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.
This part is a Barb Adapter 3/4" Barb x 3/4" Street or 1/2" Inside Slip..
The means a 3/4" Inside Diameter tube would glue over the barb side while a 1/2" pipe which is 3/4" Outside Diameter would...