(-)Flat head machine screw(Coarse Brass Unplated 3 X 12 Pitch 0.5

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): M4
• Length under head (ℓ): 15.0
• 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