100o special flat head screws have been developed for use In soft materials to distribute pressure over a larger and less angular surface. Very well adapted for use with thin aluminium, soft plastics, etc. MIL-STD-1515 "Fastener Systems for Aerospace" requires 100 degree countersunk screws.
These flat head screw(Also know as Countersunk screws) are used where the finished surfaces require a neat and flush fastening unit. The countersunk portion offers good centering possibilities.
As per ISO 5856 standards.