(-)Flat head machine screw(Coarse Brass Unplated 4 X 20 Pitch 0.7

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 diameter (d) M4
• Length under head (ℓ) 20.0
• Pitch (P) 0.7
• Head diameter (dk) Nominal 7.0 Tolerance 0,-0.5
• Head height (k) Nominal 2.6 Tolerance ±0.15
• Slot width (n) Reference 1.0
• Slot depth (t) Reference 1.4