I found these blades by chance on ebay. They happen to fit the blade holder of a very unique & special, old mat cutter that was very popular in the picture framing business in America & England in the 1960's, & 1970;s but I think that machine was made in the 1950's. It allowed new apprentices to be able to cut precision mats for professional picture framing shops. It was called the Keeton Cutter. That machine was designed to use American single edge razor blades, but over time, those blades became very low quality. the company then made a new cutting head to replace the original that used a different type of special blade. I cannot get those blades anymore. LUckily for me the Seikan single edge blade is perfect fitting in the *New* blade carrier head (that was made in the late 1970's.
Now, I may be one of the very few, or only people still using the old Keeton Kutter mat cutting machines, but with this Seikan blade (sharp too) I am able to get good results. I ordered 5 boxes of 10 blades each. I am smiling. I won the game, after all*