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General Specification for Construction and Acceptance of Mechanical Equipment Installation Projects GB50231-2009, 3.2.1 When installing bolts, the following requirements shall be met: 1. When tightening, a ratchet wrench should be used; impact methods or forces exceeding the allowable stress of the bolts are not permitted. II. The contact between the bolt head, nut, and the connected component must be tight; where specific requirements exist for the contact area and contact gap, inspections shall be carried out in accordance with the technical specifications. III. Connections that require preload shall be preloaded to the specified preload according to the assembly requirements; mechanical, hydraulic tensioning, or heating methods may be used ； The heating temperature of steel bolts shall not exceed 400°C. IV. After the bolt and nut are tightened, the bolt should protrude from the nut by 2 to 4 pitch lengths ； After tightening with countersunk screws, the heads of the screws should be embedded within the components and not protrude outward. V. For those requiring locking, it shall be locked in accordance with the specified technical requirements after tightening ； When locking with double nuts, the thin nut should be placed on top of the thick nut ； Do not use 2 identical washers under each nut. Read the 1189 Bolt Tightening Torque Chart