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Imperial and Metric scuba tools compared


A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects usually rotary fasteners, such as nuts and bolts, or keep them from turning.

[source wikipedia]

Could you compare them?

Yes, you can compare them and you will immediately notice that they are all different. Even if you were to write them down on paper in millimeters or inches.

But are they really that different/ or are there occasional sizes between them that are very close to each other?

Imperial wrench with open and closed sides.

Especially in the scuba industry we regularly deal with both sizes. For example, the ports where you connect your hoses in the first stage are almost always in sizes 3/8UNF for the low-pressure hoses and 7/16UNF for the high-pressure hoses (An example of this is Poseidon, they have some exceptions to this standard).

On the other hand, if you look at the yoke nut on the various first-stage regulators you will see that there is a mix of metric and imperial here and that this often has to do with the geographic location of the manufacturer.

Where in the world metric and imperial sizes are used.

The scuba diving industry worldwide only uses a limited number of key sizes. The most common sizes you will encounter here are:


17mm, 19mm, 22mm, 25mm, 30mm 28mm, 32mm, 34mm.


11/16inch, 3/4inch, 3/16inch, 1/4inch, 1-1/2inch, 1inch.

When we look at these sizes, the small differences and the chance of using the wrong wrench are immediately noticeable.

Confusing the metric and imperial wrench sizes can, due to the small difference, ensure that you can get the part loose, but it will also be slightly damaged during this procedure.

We, therefore, recommend that you have the most commonly used wrench sizes in both metric and imperial in your workshop.

To reduce the chance of this common mistake, At Scuba Service Tools we have tried to produce a set of extra thin wrenches to eliminate this problem as much as possible.

When combining the metric and imperial sizes we have put the two closest sizes in a single wrench.

This makes it easy to test during use, whether you are working with the right key and thus prevent damage to the diving equipment.

Thin spanner wrenches - The ultimate solution

Different sorts of thin spanner wrenches.

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