Hex socket head cap screw(Full thread(Coarse Steel Zinc plated(Silver) 8X40X40 Pitch 1.25

This is a bolt with a cylindrical head featuring a hexagonal socket.
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 known as a cap screw or socket screw. Open-end spanners and wrenches used to tighten hex bolts require clearance space around the fastener, whereas a hex key requires no such surrounding space.
For this reason, hex socket head cap screws enable work in confined spaces and allow for more compact machine designs.
Their aesthetic appearance has also led to increasing use in decorative applications.

• Hex socket head cap screw Full thread Coarse pitch
• Nominal diameter (d) M8
• Length under head (ℓ) 40.0 Thread section 40.0
• Pitch (P) 1.25
• Head diameter (dk) Max (Nominal) (1) 13 Max (2) 13.27 Min 12.73
• Head height (k) Max (Nominal) 8 Min 7.64
• Under-head fillet (r) Min 0.4
• Hex socket width across flats (S) Nominal (Nominal) 6 Max 6.14 Min 6.02
• Hex socket depth (t) Min 4
• Head chamfer (v) Max 0.8
• (1)Maximum diameter without knurling
• (2)Maximum diameter with knurling