Countersunk Allen Bolts. Allen key sizes: M3=2mm key, M4=2.5mm key, M5=3mm key, M6=4mm key, M8=5mm key. These bolts are all fully threaded.
M4 M5 M6 M8, 10.9 GRADE ZINC COUNTERSUNK CSK SOCKET CAPS SCREWS, ALLEN KEY BOLTS
M6 (6mm) GRADE 10.9 HIGH TENSILE ZINC BUTTON HEAD BOLTS SCREWS HEXAGON SOCKET
M12, 10.9 GRADE ZINC COUNTERSUNK CSK SOCKET CAPS SCREWS, ALLEN KEY BOLTS HEX
M10, 10.9 GRADE ZINC COUNTERSUNK CSK SOCKET CAPS SCREWS, ALLEN KEY BOLTS HEX
BLIND RIVET NUTS HEXAGON SHANK OPEN END FLAT HEAD M6 (6mm Ø) ZINC PLATED
M6 M8 Color zinc Plated Furniture Cross Slotted Drive Barrel Nuts Dowel Nut