Introduction of Adjustable Wrenches

An adjustable spanner or adjustable wrench – sometimes also called a ‘crescent wrench’ is an open-end wrench with one fixed jaw and another movable jaw, allowing it to be used with different sizes of fastener heads, by turning the screw that moves the movable jaw.

There are 4 major types of Adjustable Wrenches.

1. Adjustable Spanners
By far the most common type, adjustable spanners, also known as crescent wrenches, are found in almost any household.

2. Monkey Wrench
This type of adjustable wrench is typically used in large-scale projects. It is distinguished by a long handle and jagged jaw grips that stay firmly affixed to all kinds of pipes, boxes, or other objects.

3. Pipe Wrench
The pipe wrench is very similar and often confused with the monkey wrench. The pipe wrench is suitable for working on soft iron pipes and round-surface fittings. It should not be used with hex nuts because the teeth of its jaws would damage the hex head.

4. Plumber Wrench
The plumber wrench has a key ring attached to one of its handles, which is used to close the movable jaws around the pipe or fitting. Since it clasps with significant force, the plumber wrench does not have to engage the nut or bolt head it is applied to.

Adjustable Wrenches for Industrial Applications

Adjustable wrenches have become a widely used tool in the industrial environments. Many users of adjustable wrenches use these tools as a proxy or replacement to using fixed jaw spanners like combination/ring or open-ended spanners. This is not correct and therefore not recommended under guidelines issued by the Hand Tool Institute of USA, for safe use of handtools.Adjustable wrenches cannot provide necessary load and grip of fixed jaw spanner and will have tendency to slip and damage equipment and/or cause injuries.

The use of Adjustable wrenches should be avoided as far as possible and used only for light duty applications.

A recent study conducted on Hand Injuries in the United States posted on Safety Tool Box site shows that over 1,15,000 injuries are reported every year by Hand Tools.

About 25,000 people account for over 22% of the hand injuries every year, that are caused by using screwdriver and adjustable wrenches.

Torque Standards for Adjustable Wrenches.

Refer to IS standard 6149 for Single Ended Open Jaw Adjustable Wrenches/Spanner, a 300 mm or 12” Adjustable spanner is tested on a 32 mm A/F test bar. The qualifying load for a Normal Duty adjustable wrench is 480 Nm (or 49 kgf-m). If you compare this with a fixed jaw spanner, the qualifying load for a 32 mm open ended spanner is 643 Nm and 884 Nm for a Ring/Box type spanner respectively.

Therefore, adjustable wrenches are not designed for regular industrial use and do not have the strength equal to that of similar size fixed jaw spanners. Adjustable wrenches should therefore only be used for light duty applications and cannot replace fixed jaw spanners.

In its recommendations to ensure safety, Department of Industrial and Systems Engineering of North Carolina State University, advises that Adjustable Wrenches should not be used on nots and bolts.

Adjustable Wrenches in Flammable Environments, Explosives

As a first step towards safety, it is important to note is that Steel hand tools should not be used in environments with flammable vapours, liquids and solid. Even a small amount of spark caused by steel tools striking another surface, can lead to fire and potential explosion. Only Non-Sparking Hand Tools should be used. Non-Sparking Materials do not create high energy sparks and therefore prevent the risk of fire.

When handling explosives, flammable chemicals, additional care should be taken, as the nature of operations is even more critical than general industrial environments.

An article published in the magazine Drilling Contractor on 10 safety tips for hand and finger safety in Oil and Gas Drilling Operations suggests banning the use of adjustable wrenches, as the use of these wrenches has been found to be a very common cause for hand injury.


A slip of the adjustable or a pipe wrench can damage the equipment and cause a major accident. So, not only are these wrenches a serious risk to the human safety, but also are a safety hazard for the equipment, on which they are used.

Another Canadian Major Oil and Gas Company, Cenovus, in their Safety Guidelines have mentioned:

“The correct size wrench is preferred over adjustable, crescent spanner, or thumb wrenches. These wrenches can damage the fasteners and are more prone to slip off than the proper wrench.”Cenovus Safety Policy

Conclusion

It is very clear that Adjustable wrenches of any type should not be used as a replacement for fixed jaw wrenches. These wrenches should only be used in light duty applications, that too very carefully, following all the safety guidelines. Many user companies have gone to the extent of banning the use of such wrenches in their facilities, because they have found that despite several guidelines, it is a human tendency to find a way around and follow the path of least resistance. But this has resulted in many workers getting injured and their hands getting impaired for life. Human hands are very complex structures, and once damaged, can almost never be restored to their original strength and dexterity. So, hands must be protected at all costs, and not using adjustable wrenches is a major positive step in that direction.