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If you review your math, you will discover that 4/8 is exceedingly close to 1/2! The convention with straight razors is to use 1/8 increments, though some 1/16s slip in occasionally.
BTW, from...

The most common size of razors was 5/8. The 4/8 is perfectly useable and in many ways is more maneuverable. The narrower blades are a little bit more of a challenge to strop, because the narrowness...

Your link does not lead to the razor. If you can fix it, you will get better assessments of your razor. An unused Henckels razor is pretty much always a good thing. Now you just need to get it...