This vintage chisel has been made using a used triangular file. With good heat treatment it has seen a long u se, shown by the indents on the brass hoop at its butt. The triangular file profile makes it slightly bulky than paring chisels. I have used it for mortises. Decent edge retention and massive strength are its usp. The brass ring is also thick illustrates that the triangular file being used was not to save money.
The chisel is 1 cm wide. please see pics for more details