Hex socket head cap screw(Nissei Seiko(Coarse Steel Unplated 4 X 5 Pitch 0.7

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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) M4
• Length under head (l) 5.0
• Pitch (p) 0.7 Thread section (b) Reference 20
• Head diameter (dk) Max (Nominal) (1) 7 Max (2) 7.22 Min 6.78
• Shank root diameter (da) Max 4.7
• Body diameter (ds) Max (Nominal) 4 Min 3.82
• Head height (k) Max (Nominal) 4 Min 3.82
• Under-head fillet (r) Min 0.2
• Hex socket width across flats (S) (3) Nominal (Nominal) 3 Max (1st column) 3.071 Max (2nd column) 3.080
• Hex socket depth (t) Min 2
• Head chamfer (v) Max 0.4
• Full thread range 25
• Note: (1) Max for heads without knurling
• (2) Max for heads with knurling (Knurled unless otherwise specified)
• (3) 1st column: Applies to strength class 12.9. 2nd column: Applies to strength class 10.9 and below, and stainless steel.