Hex socket head cap screw(Nissei Seiko(Coarse Steel Unplated 8 X 80 Pitch 1.25

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This is a bolt with a cylindrical head featuring a hexagonal recess.
A hex key (Allen wrench) is used for tightening. Although classified as a bolt, it is most commonly used without a nut.
It is also referred to as a cap screw or socket screw. Unlike open-end spanners or wrenches used to tighten hex bolts, which require clearance space around the fastener, a hex key requires no such surrounding space.
Therefore, the use of hex socket head cap screws enables work in confined spaces and contributes to the miniaturization of machinery.
Their appearance has also led to increasing use in decorative applications.

• Hex socket head cap screw Nissei Seiko Coarse pitch
• Nominal diameter (d) M8
• Length under head (ℓ) 80.0
• Pitch (p) 1.25 Thread length (b) Reference 28
• Head diameter (dk) Max (Nominal) (1) 13 Max (2) 13.27 Min 12.73
• Shank root diameter (da) Max 9.2
• Body diameter (ds) Max (Nominal) 8 Min 7.78
• Head height (k) Max (Nominal) 8 Min 7.64
• Under-head fillet (r) Min 0.4
• Hex socket width across flats (S) (3) Nominal (Nominal) 6 Max (Column 1) 6.095 Max (Column 2) 6.140
• Hex socket depth (t) Min 4 Head chamfer (v) Max 0.8 Full thread range 35
• Note: (1) Max without knurling
• (2) Max with knurling (Knurled unless otherwise specified)
• (3) Column 1: Applies to strength class 12.9. Column 2: Applies to strength class 10.9 and below, and stainless steel.