The screws are the same size for the center post and negative holes in the deck. Link is directly from Peter's(pdib) thread(ECF/muzichead)
Set Screw - 18-8 Stainless Steel Cup Point M2(Metric 2mmDiam), 2.5mm Long, 0.4mm Pitch - Hex key 0.9mm or 0.035"
McMaster-Carr