What is the torque range for hand-tightening screws?
2 Answers
The maximum torque range for a normal human hand is 60N—120N. Below are the extensions for using a wrench torque: 1. Select an appropriate range: When using a torque wrench, first select a torque wrench with a suitable range based on the requirements of the workpiece being measured. The measured torque value should not be less than 20% of the wrench's range during use. A too-large range is not suitable for reinforcing small torque components, and a small-range torque wrench should never exceed its range. 2. Pre-use inspection: Before using the torque wrench, first connect the square drive of the wrench to the auxiliary accessories to ensure the connection is secure. Before applying torque, set the required force value and lock the tightening device. Adjust the direction switch to the tightening direction, then quickly operate the wrench 5-6 times in succession to allow the special lubricant inside the wrench components to fully lubricate, ensuring the torque wrench is more accurate and durable. 3. Control the range: During measurement, hold the handle within its effective range and apply force slowly in the direction perpendicular to the torque wrench's housing until you hear a "click" sound from the torque wrench. This indicates that the torque wrench has reached the preset torque value, and the workpiece has been adequately tightened. Immediately release the force afterward to avoid damaging other components.
The torque applied when tightening screws by hand varies from person to person, mainly depending on screw size, tools used, and individual strength. Generally, when tightening manually with a screwdriver, the torque may only be a few Newton meters (Nm), such as 3-5 Nm for small screws. However, with a wrench or socket, a strong person can achieve 20-50 Nm. In automotive repairs, wheel bolts typically require 80-120 Nm, which is difficult to achieve precisely by hand, often resulting in over-tightening or under-tightening. Over-tightening may damage threads or components, while under-tightening can lead to loosening screws, compromising driving safety. I've encountered many cases where relying on feel caused issues, so it's best to use a torque wrench for accuracy. Repair manuals specify exact values, such as 15 Nm for a certain model's hood bolts, but remember that manual tightening is only a temporary solution—critical areas should be checked by a professional shop.
