slim blades

[JOB15]

I have this pipe razor, 9mm in width. I have quite a few of these type blades and I cant figure out what there deal is.

Are or were they used primarily for trimming?

How are you supposed to hone them, I would need to half the tape length ways to start with.

This one is German I'm guessing, although the writing on the reverse of the tang does not seem German to me.