These M2 (2mm thread) bolts are made from 12.9 grade carbon steel. They have a very high tensile strength. The hex socket in the head of the bolt is a 1.5mm size.

Where possible, I will always choose block head bolts over pan head bolts for my builds. Pan head bolts do offer a very small weight saving, but this is usually negligible. Block head bolts have a bit more hole depth for the hex bit to seat into making them less likely to strip the hex recess when undoing them. This is more relevant to M2 bolts than M3 bolts. Block head bolts can also be easily gripped with pliers to be unscrewed if you do happen to strip the hex recess.