How to use a centre head

Shop for Protractor Sets

Step 1 – Place combination square set on object

Place the combination square set on the circular object with the centre head attached.

Step 2 – Mark diameter line 

Mark the diameter of the object along the rule.

Step 3 – Mark second diameter line 

Move the combination square set and mark a second diameter line (you may choose to do this at roughly 90 degrees to the first line). Where the lines cross each other should mark the centre of the object.

Step 4 – Identify centre of circle (if necessary) 

Sometimes the object may not be an exact circle. When this happens, marking more than two diameter lines may show that they do not all cross at the same point. You can then make a judgment on where the centre actually is.