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What is an open-ended spanner?

What is an open ended spanner?

Open-ended spanners are versatile, single-piece tools that can be used on most types of fasteners around the home and across the industries. They are the characteristic spanner type!


Their head has two jaws forming a U-shaped profile with two parallel flat sides. 


The opening between the jaws is the width of the fastener head so the tool can be slipped around the fastener from the side. This width indicates the size of the tool in metric and AF (‘across flats’) imperial measurements.

How do open ended spanners work?

The flat sides make contact with two of the parallel flat sides of a fastener and push against them to turn it.


Open-ended spanners can turn any fasteners with two parallel flat sides (e.g. fasteners with square, hexagonal or octagonal heads).

What are the different sizes of open ended spanner?

Open-ended spanners can have one head or two heads (one at either end of the shaft). Two-headed spanners will have two different sizes, either one to two size differences (e.g. 16mm and 17mm) or two common sizes (e.g. 13mm and 16mm).


Sizes of open-ended spanners range from 4mm to 50mm or 5/32″ to 2″ and the length of the tool ranges from 100mm (4″) to half a metre long (19½”). The tool gets longer as the head size gets bigger to provide enough leverage to turn the larger fasteners.


Heads of open-ended spanners are usually at a 15 degree angle to the shaft. This allows an increase in movement, creating a larger turning arc in enclosed places when the spanner is flipped over.

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