These Italiam-made blades are OEM parts for Galfre and Terra drum mowers. The blades have 2 edges for better economy. When blades get dull, just switch the blades on the right drum to the one on the left and vice-versa.
All blades on a drum should be replaced at once to maintain proper balance of the drum.
These high quality blades will maintain their edge better than cheap aftermarket blades.