(-)Flat head machine screw(Coarse Stainless steel Unplated 3 X 20 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 diameter (d) M3
• Length under head (ℓ) 20.0
• Pitch (P) 0.5
• Head diameter (dk) Nominal 5.5 Tolerance 0,-0.5
• Head height (k) Nominal 2.0 Tolerance ±0.15
• Slot width (n) Reference 0.8
• Slot depth (t) Reference 1.1