What accuracy are engineer’s squares made to?

29th February 2020


What accuracy are engineer’s squares made to?


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		In the UK, engineer’s squares have to be manufactured to British standard BS 939 as set out by the British Standards Institution (BSI). BS 939 divides engineer’s squares into 3 grades of accuracy: Grade AA, Grade A and Grade B, with Grade B being the least accurate, and Grade AA the most. Grade B is often referred to as being workshop grade, and whilst it is the least accurate BS 939 grade, it is the one most commonly used. Grade AA and A are only required for laboratory use or for checking and calibrating other tools. The BSI Kitemark is a registered trademark of The British Standards Institution and the use of it is with kind permission.

		In order to meet BS 939, an engineer’s square must meet or exceed the requirements set by BS 939 in size, material and manufacture, finish, accuracy, rigidity, general features of design and protection against climatic conditions. Engineer’s squares that do this are allowed to display the BSI kite mark logo. The BSI Kitemark is a registered trademark of The British Standards Institution and the use of it is with kind permission.

		Why is BS 939 important?
		BS 939 is important to engineer’s squares as it provides a simple and clear way of comparing the accuracy of squares to one another. It also enables all users of a particular grade of square to maintain the same level of precision and accuracy in their work, both within and outside the UK.

		What is DIN 875?
		DIN 875 is the standard to which engineer’s squares are made in Europe. You will often see engineer’s squares advertised as conforming to both BS 939 and DIN 875.

		Do engineer’s squares require calibrating?
		As with any tool that has standards of accuracy, it is important that the accuracy of an engineer’s square is properly maintained. The United Kingdom Accreditation Service (UKAS) says an engineer’s square should be calibrated in house, on a yearly basis and by a UKAS accredited organisation once every five years in order to maintain its accuracy.