This European Standard specifies the profiles of thread for all the screw deck finishes for metallic, plastic and metallo-plastic closures.
The depressed threads could be used on continuous thread finishes to reduce the thread depth at and adjacent to the mould parting line.
Depressed threads are only used on > 28 mm Roll-On Pilferproof (ROPP) type finishes where the closure is formed on the neck finish.