Armored Flottrop: Age?

[S.A.M. Martin]

FLOTTORP:

I'm having trouble with this propeller. Got any ideas?

The stamp on it appears to be KS 55. I've never heard of this. Have you?

[Dave]

It looks like an older decal, but the design looks more like 30's/40's. I don't see anywhere that Flottorp had a "KS55" design number. It also looks as if the prop has been partially refinished.