MTH Series - #7 underlayment screw, hi-lo thread, sharp point, modified trim head w/nibs, gray phosphate finish. CB3BLG Series - #10 fiber cement board to wood or steel (33, 27, 18 mils / 20,22,25 gauge), coarse thread, type 17 point, .375 ribbed bugle head, C3 mechanical galvanized corrosion protection. CBSDG158PS - #8 screw, #2 drill point, Quik Guard or TufCote corrosion protection, countersink nibs, phillips drive; designed to fasten fiber cement siding to steel framing (54, 43, 33, 27, 18 mils / 16, 18, 20, 22, 25 gauge)