①,screw threads: For bolts and screws as forged or faced under the head, and for nuts as forged, the screw threads shall be Unified Coarse (UNC) in accordance with BS 1580, "Unified screw threads", as specified by the purchaser. For bolts and screws faced under the head and machined on the shank and for machined nuts the screw threads shall be Unified Coarse (UNC), Unified Fine (UNF) in accordance with BS 1580, "Unified screw threads", as specified by the purchaser. |