: Split lockwashers usually require a hardness of Rockwell C 42–50, while flat washers are softer at Rockwell B 60 maximum. Comparison of Common JIS B 1188 Sizes
JIS B 1188 PDF can be obtained from various sources, including: jis b 1188 pdf
The standard specifies requirements for cross-recessed head screws with captive washers . These are often referred to as "Sems" screws, where a washer is permanently attached to the screw blank before the threads are rolled, preventing it from falling off. Quick Reference for JIS B 1188 : Split lockwashers usually require a hardness of