Cross recessed(+)Binding head machine screw(Coarse Stainless steel Unplated 3.5 X 6

The head is trapezoidal in shape with a rounded top surface. The head diameter is approximately 1.1 to 1.2 times larger than that of a pan head machine screw of the same nominal diameter.
Because the bearing surface area against the material is larger, it is effective in preventing the seating surface from sinking into the material.
It is also used in applications where a truss head would be too large in diameter, and like the pan head, it is a machine screw that can be used in a wide variety of applications.
The large head diameter not only helps prevent the seating surface from sinking into the material, but is also convenient for concealing the mounting holes in the fastened material.
It gives a slightly sleeker impression than a pan head machine screw, so it may also be chosen for aesthetic reasons.

Machine Screw Head Dimension Chart 　Bind Machine Screw Encyclopedia
Bind Machine Screw (Bind Head)

• Cross recessed (+) binding head machine screw coarse pitch
• Nominal thread diameter (d) M3.5
• Length under head (ℓ) 6.0
• Coarse pitch (P) 0.6
• Cross recess number 2
• Head diameter (dk) Nominal 7.3 Tolerance 0, -0.5
• Head trapezoidal section height (k) Nominal 1.5
• Head dome section height (f) Nominal 0.7 Tolerance ±0.15
• Head height (k+f) Nominal 2.2 Tolerance ±0.2
• Cross recess (m) Reference 4
• Cross recess depth (q) Max 1.83 Min 1.30