The plastic drum seals are polypropylene made cap seal, designed to lock directly onto plastic bung on HDPE drum barrels under specification guidance. These two combined to be the basic cap system for tight head poly drum, either with 2'' and 3/4'' NPT openings or with 2'' NPT and 2'' buttress openings.
Same as other types of drum cap seal, the plastic drum seals protect the filling content from contamination and pilferage.