This part of ISO 965 specifies deviations and limits of sizes for pitch and crest diameters for ISO general purpose metric external screw threads conforming to ISO 262 having a basic profile according to ISO 68-1. External screw threads according to this part of ISO 965 are intended to mate with internal screw threads tapped with tolerance position H or G after hot dip galvanizing. The limits of sizes for the tolerance quality specified are derived from tolerances specified in ISO 965-1 and the fundamental deviations according to the following formula: esaz = 2(300 + 20P) where es is expressed in micrometres; P is expressed in millimetres. Products made with thread tolerances in accordance with this part of ISO 965 may show failure at lower ultimate tensile loads than those specified in ISO 898-1 due to reduction of the stress area. External screw threads with thread tolerances according to this part of ISO 965 must not be mated with internal screw threads with thread tolerances according to ISO 965-5 because such combinations will create severe risk for thread stripping. NOTE If the tolerance class 6az is not specified the external screw threads are to mate with internal screw threads with tolerance position 6AZ if the products are centrifuged and with hot-dip galvanized internal screw threads with tolerance position 6AX if the products are not centrifuged.