Plumbing fittings are classified using the standard notation described and illustrated below.
slip glues into pipe
sp glues to another fitting
insert tubing barb
fipt female threads
mipt male threads
Slip fittings are glued to pipe and may have male or female threads on one end. All are classified as "Glue and Thread." Examples: S X S, S X mipt, S X fipt, etc.
All fittings with a barbed end for flexible tubing are classified as "Insert/Barb." Insert fittings may also have a male, female or barb at the other end. Examples: I X I, I X mipt, I X fipt, etc.