It’ has the makers name which is MOORE AND WRIGHT Sheffield England, (A TOP MAKER IN ITS DAY) dated 1940 and next to the date is the government Broad arrow, which shows a quality made item to government standards, hence the government put their mark on it, final marking shows the square was hardened.

I have put 2 rulers along 2 edges to show the size of the square.

My father was working in the aircraft industry from 1939 to 1945 during the WW2 period as a toolmaker which was classed as a reserved occupation, hence government work, and the broad arrow to verify 

A top quality item with history to show.

No returns, no sales outside U K 

Seller has 100 % feedback ,,,,,,,,,,,,,,,,,,,,,,,,, thanks