(-)Flat head machine screw(Coarse Steel Unplated 2 X 5

The head of a round machine screw is nearly hemispherical in shape, similar to today's truss head machine screw. The flat head machine screw has a low-profile cylindrical head. It was commonly manufactured in the past due to its simple production method.
Machine Screw Head Dimensions List　Encyclopedia of Round & Flat Head Machine Screws

• Slotted (-) flat head machine screw coarse pitch
• Nominal thread diameter (d) M2.0
• Length under head (ℓ) 5.0
• Pitch (P) 0.4
• Head diameter (dk) Nominal 3.5 Tolerance 0,-0.4
• Head height (k) Nominal 1.3 Tolerance ±0.1
• Slot width (n) Reference 0.6
• Slot depth (t) Reference 0.7