Flange buttonHex socket head cap screw(Coarse Steel Unplated 8 X 20(P=1.25 Pitch 1.25

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JIS B 1174
A hex socket button bolt characterized by its rounded head shape.
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 earlier, and the "JIS Standard," which was subsequently established in accordance with ISO. The two types differ in head dimensions.
3S Standard (Manufacturers: Tokokisha Kinzoku SS, Gosho SS, Chubu Raiji, Kyokuto SS)
JIS Standard (Manufacturers: Nissan Neji, Ansco, Alps Seiko)

Button CAP Standard Comparison
Thread Pitch List

• Flange button hex socket head cap screw (coarse pitch)
• Nominal diameter (d): M8
• Length under head (ℓ): 20.0
• Pitch (P) coarse pitch: 1.25
• Head diameter (Φdk): Nominal 12.6, Tolerance 0,-0.43
• Neck diameter (Φda): Max 9.2
• Hex socket width across corners (e): Min 5.72
• Head height (k): Nominal 4.4, Tolerance 0,-0.30
• Under-head fillet (r): Min 0.4
• Hex socket width across flats (s): Nominal 5, Tolerance +0.140,+0.020
• Flange section diameter (Φw): Nominal 17, Tolerance 0,-0.6
• Hex socket depth (t): Min 2.6
• Flange section thickness (h): Min 1.4