When selecting an engineer’s square, you should think about the following:
The size of the workpiece
The accuracy level you need to attain
Any additional features you may need (e.g. stock, graduation marks)
Whether to purchase individually or in a set
The size of workpiece
Engineer’s squares come in a range of sizes, and you should select an engineer’s square that is of an appropriate size for the workpiece you will be using it on.
The size refers to the measurement along the inner length of the blade. This can range in size from 50mm (2″) to 1000mm (40″) in length.
The blade of a square will need to be long enough to cover the distance you need to mark on the workpiece, but not longer than is necessary.
Using an engineer’s square that is too large for the workpiece is likely to make the job more awkward, while using a square that is too small will mean you cannot mark the full length of the lines you need to, and extending the lines will affect their accuracy.
Accuracy
For most uses, a Grade B engineer’s square, often referred to as workshop grade, is more than accurate enough.
More accurate Grade A and AA are only needed for use in laboratory conditions and for calibrating other tools.
With or without a stock?
An engineer’s square with a stock can be laid on its side and butted up against the side of a workpiece. This often makes the tool easier to use, giving more accurate results.
If you are using a large engineer’s square, then one with a stock will have a thin blade that could be bent or damaged more easily. In which case, you may prefer to use an engineer’s square without a stock but with a thicker blade.
Graduation marks
Graduation marks on the blade of an engineer’s square allow you to measure out the length of the line you wish to place on the workpiece, using just the one tool. This can be a handy feature to have, as trying to hold a ruler and engineer’s square accurately whilst marking the workpiece at the same time can be tricky.
Buying engineer’s squares individually vs a set
An engineer’s square set will normally comprise of four engineer’s squares each of a different size. This will allow you to accurately mark out workpieces of different sizes.
Sets of engineer’s squares often come with their own storage case, which is a great way of keeping your engineer’s squares separate from your other tools, preventing them from becoming damaged.
If you only need an engineer’s square to mark one particular size workpiece, then it would make sense to purchase just the one engineer’s square. However, if you intend to use engineer’s squares for marking more than one size of workpiece then it is a good idea to purchase a set.