Fasteners such as head bolts and lug nuts help securing different parts that are under constant tension and stress. They come in different sizes and levels of hardness. Screw thread type fasteners must be tightened to a specific amount of torque. Hence, we use Torque Wrenches to do this job. But an important question is: What Size Torque Wrench Do You Need?
In this guide, we will see briefly about Torque Wrenches, types of torque wrenches and what size torque wrench to use.
An Overview of Fasteners and Torque
Any decent automobile technician must know about different types of fasteners (nuts and bolts), tightening procedures, what size torque wrench to use, etc. Speaking of tightening fasteners, we should not over tighten or under tighten it as it can damage or break or become loose over time.
But how do we make sure that a fastener is tightened properly? This is where the torque specifications of nuts and bolts come handy. As it is difficult to precisely measure the tightening force, what we do is use the predetermined torque values from manufacturers or user manuals.
Here torque is nothing but the twisting force we apply on the bolt/nut to create a tension so that the bolt helps the surfaces be clamped together. We usually measure torque in terms of foot-pound (Torque = Force × Length).
We can define a ‘foot-pound’ of torque as the force applied on a shaft by a 1-foot long perpendicular level with a 1-pound weight attached to the outer end of the lever. Coming to the metric World, we use a similar explanation to express a Newton-Meter of torque.
What is a Torque Wrench?
We have the fastener (nut or bolt) and its torque specification. How to use them? Torque Wrenches are the tools for this job. It is also known as a Tension Wrench and we use it to tighten fasteners to a predetermined torque.
For example, take a cylinder head bolt. Its manufacturer recommends a torque for this bolt so that:
- It will provide enough clamping pressure
- Will not come loose
- It will also be not so tight and risk breaking of the bolt or stripping the threads
Lug nuts are another important fastener that should always be tightened with a Torque Wrench. Using predetermined torque on a lug nut ensures that it is tightened to the right amount and also evenly. In fact, one of the easiest ways to understand and learn to use a Torque Wrench is to install and tighten lug nuts.
The three things you have to consider when buying a torque wrench are:
- Drive Size
- Torque Range
You have to take very good care of torque wrenches as they are precision tools. Most of them loose their precision over time and you have to re-calibrate them directly from the manufacturer or from a reputable third-party service.
Types of Torque Wrenches
There are several types of torque wrenches depending on how they read the torque. Some torque wrenches directly display the reading using a dial or a digital display. Other types use some sort of sensor based signaling system to indicate the user when they reach the predetermined torque.
Here are some popular Types of Torque Wrenches:
- Click Type
- Beam Type
- Dial Type
- Slip Type
- Split Beam Type
Click Type Torque Wrench
One of the most popular types of torque wrench is a Click Type Torque Wrench. It is very easy to use and even storing/maintenance is also simple. Thus, most automobile technicians prefer to use this type of torque wrench.
Its working is also very simple. There is a preloaded snap/click mechanism with a spring and when it reaches the specified torque, the mechanism releases making a ‘click’ sound.
Setting the torque and using the wrench is very easy. Simply rotate the micrometer handle to set the torque and pull on the handle until you hear the click sound.
Beam Type Torque Wrench
This is the simplest and least expensive type of torque wrench. In a Beam Type Torque Wrench, the main handle is made up of spring steel beam that bends/flexes under tension. A small pointing structure (tiny rod or needle) indicates the amount of torque using a scale on the head.
When we apply force on the handle to tighten a nut, the flexible arm bends and deflect the needle on the scale. You can then precisely tighten the nut based on the reading from the scale.
You have position yourself directly in front of the scale as parallax error is a major issue with this type of torque wrench and scale.
Dial Type Torque Wrench
Even though this is not as popular as the previous two types, the Dial Type Torque Wrench is an easy to operate and calibrate option. When you tighten a fastener, a pointer will move up the scale to indicate the amount of torque.
What most technicians do is rotate the bezel face to the required torque, zero out the dial and then pull the wrench to obtain the proper torque.
Electronic / Digital Torque Wrench
Now-a-days, almost every tool accessory is electronic. The same is the case with torque wrenches. Electronic/Digital Torque Wrenches are very easy to use. Simply set the desired torque using buttons and pull the handle/lever.
The internal circuit will detect the torque and if it matches the value we entered, it starts a beep. There are even advanced digital torque wrenches that store the torque settings.
What Size Torque Wrench Do You Need?
Torque Wrenches come in different drive sizes, which indicate the square drive that accepts the socket, adapter or extension. Some popular torque wrench sizes are: 1/4”, 3/8”, 1/2″ and 3/4″ – 1”. So, the obvious question is: what size torque wrench do you need?
Here is a table that specifies some popular torque wrench sizes along with the suitable bolts or screws.
|Torque Wrench Size||Bolt or Screw Size|
|1/4||4 – 48|
|5/16||6 – 40|
|11/32||8 – 36|
|3/8||10 – 32|
|7/16||1/4 – 28|
|1/2||5/16 – 24|
|9/16||3/8 – 24|
|5/8||7/16 – 20|
|3/4||1/2 – 20|
|7/8||9/16 – 18|
|15/16||5/8 – 18|
|1-1/16||3/4 – 16|
|1-1/4||7/8 – 14|
|1-7/16||1 – 14|
If you want a much clear explanation, then read along to find out what size torque wrench will suit you.
- Motorbike technicians need two basic types of torque wrenches: a 3/8” inch-pound torque wrench and a 1/2″ foot-pound torque wrench. The 3/8” torque wrench that reads in inch-pounds is suitable for handling small nuts and bolts such as fork pinch bolts and brake caliper bolts. The larger 1/2″ torque wrench that reads in foot-pounds is suitable for larger nuts and bolts such as axle and sprocket bolts.
- The 1/4″ torque wrench is a small drive wrench that is suitable for small automobiles (mopeds, scooters and motorbikes). A typical 1/4” Square Drive Torque Wrench can provide 4 to 21 foot-pounds of torque. This is suitable for small motors, garden equipment etc.
- Some engine parts such as spark plugs need a light torque. For this, a 3/8” torque wrench is a good choice. This is an extremely popular size of torque wrench among all automobile technicians (cars, trucks and motorbikes). A typical 3/8” square drive torque wrench can provide 15 to 75 foot-pounds of torque.
- We are now moving to larger drives. Engine mounts, axles and sprockets use large size bolts with significantly higher torque values. A 1/2″ torque wrench can provide 30 to 250 foot-pounds of torque and it is ideal for all the job that we mentioned before. You can work on wheel lug nuts, vehicle suspension with this torque wrench.
- Larger torque wrenches with drive sizes in the range of 3/4″ to 1” are a must have if you work on large trucks (semis, construction etc.), industrial jobs, aviation industry.
Torque wrenches are very useful tools in automobile industry. Using them, we can accurately set the torque of a lug nut, vehicle suspension, a trans-axle mount or even an engine mount. As torque wrenches are available is a variety of drive sizes, its extremely important to understand what size torque wrench to use for a particular job. In this guide, we saw about torque wrenches, different types of torque wrenches and also some popular torque wrench drive sizes and their applications.