Hex head cap screws, commonly referred to as just "bolts" feature a hex head and come in coarse and fine threads. Metric hex cap screws use a DIN numbering system to denote fully or partially threaded. Grade 8.8. hex cap screws are made from quenched and tempered medium carbon zinc plated steel. Grade 8.8. is comparable to imperial Grade 5. M5-M16 diameters have a minimum tensile strength of 116KSI and M18-M39 diameters have a minimum tensile strength of 120KSI.