I. Basic Appearance and Feel Judgment
1. Fit: The nut's end face should be completely flush with the workpiece surface, with no visible gaps or tilting.
2. Tightening Feel: Tighten by hand until it can't be tightened any further, then apply 1/4 to 1/2 turn with a regular wrench. The nut should not feel slippery or spin freely.
3. Thread Allowance: After tightening, 2-3 threads should be visible at the end of the bolt, ensuring the effective engagement count is met.
II. Operation for Different Sizes
1. M6 and smaller sizes: Use a regular adjustable wrench, applying even force with one hand, without using extra body weight, until it is completely tight.
2. M8 to M16 medium sizes: Use a corresponding size open-end wrench, applying even force with both hands until the wrench slightly deforms and the nut stops turning.
3. For M18 and larger nuts: Use an extended lever arm socket wrench. A single person should stand steadily on the ground and apply force without using jumping or stomping to generate impact.
III. Auxiliary Verification Techniques
1. Marking Line Verification: Draw alignment marks on the nut and workpiece surface. Gently turn the nut with the wrench. If the marks are aligned, the nut is not loose.
2. Symmetrical Tightening: When multiple nuts are used to secure the same component, tighten them two rounds in a crisscross pattern to ensure even force distribution across all nuts.
3. Tapping Verification: Gently tap the side of the nut with a small hammer. A clear, metallic sound indicates proper tightening; a dull thud indicates incomplete tightening.
IV. Safety Precautions
1. Do not use body weight or step on the wrench to apply force, as this may overload the thread, cause breakage, or slip and injure the person.
2. This method is not recommended for critical load-bearing areas. Use a torque wrench for subsequent checks when possible.
3. After installation under vibration or heavy load conditions, the nuts should be checked again after 24 hours to see if they are loose.
