I was ordering a few bits from AliExpress last week and came across some pan head screws in stainless that are made to GB823 standard. Not one that I am familiar with, so just to make the order big enough to avoid postage cost, I ordered a few in M5 and M4.
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They have a smaller head compared to the DIN standard screws but the head is slightly thinner. Probably risky under high preload settings but perfectly adequate for holding carbs and other non stressed bits together. Finish is reasonable too so not much buffing needed to shine them up a bit. Head diameter is the same as jis in the M5 size.
Regards
Dave