Hex socket head cap screw(Coarse Steel Unplated 20 X 40(P=2.5 Pitch 2.5

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This is a bolt with a cylindrical head featuring a hexagonal socket.
Tightening is performed using a hex key (Allen wrench). Although classified as a bolt, it is most commonly used without a nut.
It is also known as a cap screw or socket screw.
Spanners and wrenches with jaws for tightening hex bolts require clearance space around the work area, whereas a hex key requires no such space.
For this reason, hex socket head cap screws enable work in confined spaces and allow for more compact machine designs.
Their appearance has also led to increasing use in decorative applications.


Cap Bolts　
Representative Standard Dimensions for CAP Screws　
Hex Socket Head Cap Screws　

• Hex socket head cap screw (Coarse pitch)
• Nominal diameter (d) M20
• Length under head (ℓ) 40.0
• Pitch (P) 2.5
• Thread length (b) Reference 52
• Head diameter (dk) Max(1) Nominal 30 Max(2) 30.33 Min 29.67
• Neck diameter (da) Max 22.4
• Body diameter (ds) Max Nominal 20 Min 19.67
• Hex socket width across corners (e) Min 19.437
• Head height (k) Max Nominal 20 Min 19.48
• Neck fillet (r) Min 0.8
• Hex socket width across flats (s) Nominal Nominal 17 Max 17.230 Min 17.050
• Hex socket depth (t) Min 10
• Head chamfer (v) Max 2
• *Max(1) Maximum diameter without knurling / Max(2) Maximum diameter with knurling