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.