These are from Choate and are $6.30 on their web store. I see them for $9 to $10 on e-bay and other sites. Made of exotic fiberglass filled plastic. These letter openers can be driven through 1/2 inch plywood with minimal damage, needing only to be resharpened. Measure 1 3/16 inch wide, 7 3/4 inch long and blade length of 4 1/2 inch. Weight only 2 ounces. These letter openers can be carried under a watch band, in a sock, shirt or jacket. It can also be worn on a lightweight cotton string around the neck or taped anywhere on the body.
I was in the Corporate world for a short time after retiring and could not bring any kind of weapon into the Headquarters. I had one of these "Letter Openers" in my brief case, just in case.
You are responsible to know if this item is legal in your state.