Torque wrench

Torque spanner: what you need to know

Torque wrenches are tools which help to tighten a threaded fastener with a precise torque. They are used for assembly maintenance which requires the tightening torque stated by the manufacturer to be observed.

What are the types of torque wrenches?

• Beam. They are characterised by a low price and aren’t fitted with a limiter. The amount of torque is controlled visually which isn’t very comfortable when working with fasteners in hard-to-reach places. Besides, the error of measurements might range between 5% and 20%. Tools of this type may have a fixed arrow or dial gauge indicator.
• Ratchet. They are characterised by high precision. Depending on the type of the feedback:
  • Click. They are most widely spread and fitted with a pre-set scale. When the pre-set amount of torque is reached, parts of the transmitting mechanism start to slip producing a clicking sound. Such tools are comfortable to use in places which are difficult to reach as there is no need to control the torque. The error of measurements of these tools usually isn’t higher than 8%.
  • Digital. Fitted with an LCD display which shows real-time torque readings. When the required amount is reached, there is a sound, visual or vibration signal. Electronic torque wrenches feature the utmost precision: the error of measurements is about 1%. Have a high price.

Operating principle

Beam torque wrenches comprise a lever arm with a scale on it and a fixed indicator. When the fastener is being tightened, the scale and the pointer diverge at an angle equal to the applied force. It shows the amount of torque. Tools with a dial gauge indicator have a similar design but they are fitted with a special spring dynamometer.

Slipper torque wrenches comprise a ratcheting mechanism and a spring. It is compressed to the amount equal to the preset torque affecting the elements of the mechanism. When the fastener is being tightened, a special clicking mechanism goes off signalling that the preset torque has been reached. Electronic tools are designed in a similar way but a card and sensors perform the regulation and force transmission.

Tips on using torque wrenches

If the wrench can be calibrated, you have to adjust it in a corresponding way. The detailed sequence of operations is described by the manufacturer in the tool manual. The maximum allowable load which the product intended for is also stated there. It is strongly recommended not to exceed this amount: firstly, the tool might break, secondly, when it is used in its limit positions, the readings might be inaccurate.

It is desirable not to loosen overtightened and stuck fasteners with a torque wrench. To perform such works, you should use various spanners and special penetrating agents which dissolve corrosion. It is not allowable to use electronic tools at very low temperatures.

It is necessary to keep the instrument in a dry and clean room. A calibrating handle, if there is any, should be set to the zero position. This will allow you to protect the spring from damage.

It is recommended to have your tool checked and calibrated once a year, preferably in a service centre.

AUTODOC: convenient online shopping

To be confident in the quality of the purchased products, we recommend you to buy a torque wrench in our online shop. Contact our specialists to find tools appropriate for operating conditions and technical specifications of the car. With their help, placing an order will take you very little time.