according to ISO 898, part 1
The revised standard as of April 2009 has been for the application for bolts, screws and studs with specified property classes – coarse thread and fine pitch thread.
Fasteners according to a product standard with reduced loadability need to be marked with property class preceded with the digit «0». The objective of the revised head marking is an indicative instruction for the assembly process. The user can further look up for additional notes in the Bossard catalogue. The revised head marking is a defined identification in accordance to the revised standard.