ButtonHex socket head cap screw(Ansco(JIS(Coarse Steel Chrome(Silver) 3 X 8 Pitch 0.5

JIS B 1174
A hex socket button head cap screw characterized by its rounded head profile.
Also known as a button cap screw.
Compared to a hex socket head cap screw of the same size, the hex socket is smaller.
There are two types of button cap screws: the "3S Standard," an industry association standard (union standard) that was established first, and the "JIS Standard," which was later established in accordance with ISO. The two types differ in head dimensions.
3S Standard (Manufacturers: Tokosha Metal SS, Goshō SS, Chubu Raši, Kyokuto SS, Ansco (Maruko))
JIS Standard (Manufacturers: Nissan Neji, Ansco, Alps Seiko)
Button CAP Standard Comparison

• Button cap screw Ansco JIS Coarse pitch
• JIS B 1174
• Nominal diameter (d) M3
• Length under head (L) 8.0
• Coarse pitch 0.5
• Head diameter (dk) Max 5.70 Min 5.40
• Head height (K) Max 1.65 Min 1.40
• Hex socket width across flats (S) Nominal 2 Max 2.080 Min 2.020
• Hex socket depth (t) Min 1.04