Our other sites:

What are the parts of an engineer’s straight edge?

What are the parts of an engineer’s
straight edge?

Shop for Engineer’s Straight Edges

Parts of an engineers straight edge, working face, ribs, weight saving holes, supporting points, bowed back

Working face

The working face of an engineer's straight edge highlighted in red is the area that is place in contact with the workpiece The working face of an engineer’s straight edge (highlighted in red) is the flat surface that is placed in contact with the workpiece.

‘I section’ and ‘rectangular’ straight edges have two working faces.

Supporting points

Supporting points are positioned 2/9 of the length of the straight edge in from the ends of the working face The supporting points, or ‘feet’ of an engineer’s straight edge, are positioned on the opposite side to the working face, slightly in from the ends of the tool. By positioning the supporting points here, the straight edge will experience the minimum natural deflection of the working face (deflection due to the weight of the tool itself).

Additional features

Weight saving holes evenly distributed along the length of an I section engineer's straight edge

Weight saving holes

Weight saving holes are found mainly on large cast iron and steel straight edges. The holes are positioned along the length of the straight edge, keeping the weight to a minimum without affecting the rigidity and accuracy of the straight edge.

Weight saving holes on granite straight edges often act as supporting points for lifting them as well. On some very large granite straight edges, the weight-saving holes are also the supporting points that can be used for lifting the straight edge using a crane.
Ribs on a bow shape engineer's straight edge help save weight whilst maintaining rigidity and accuracy


Ribs (highlighted in red) are often used in conjunction with weight saving holes to minimise the weight of the straight edge whilst maintaining the accuracy required.

Ribs distribute internal stresses (created by changing atmospheric conditions) evenly across the straight edge.

Knife edge engineers straight edge with centimetre and millimetre graduated measurements along the bevelled edge


These are marks of measurement sometimes placed on the side faces of a rectangular or knife edge straight edges. They allow the straight edge to be used as a ruler.

Wonkee Donkee "I had to go to university to have a graduation, if you just needed marks down your side then any old Zebra could graduate!"
Rectangular straight edge being used for measuring Bowed and I section straight edges are not used for measuring, only checking the surface of objects are flat. So graduation marks are not found on I section or bow shaped straight edges. If you need a straight edge with graduation marks, you will have to use either a rectangular straight edge or a knife edge straight edge.
Hanging holes on a knife edge engineer's straight edge are used to store the straight edge

Hanging holes

Some smaller and thinner rectangular and knife edge engineer’s straight edges have a hanging hole on one end. This allows the straight edge to be hung up when not in use and minimises forces through the working face, so reducing any possible distortion of the working face.

Wonkee Donkee Tools