National Music String Co. Black Diamond Strings Box with 4 Strings (1930s-1970s)

Black Diamond Strings on a Catalog guitar
That's pretty high cotton whoever you are
You break one, you change one, that's as good as it gets
You can play all year long on two or three sets...
Guy Clark, "Black Diamond Strings"

Here is a vintage Black Diamond Strings box with 4 packs of strings (3 unopened). Black Diamond Strings were manufactured by the National Musical String Company in New Brunswick, NJ beginning in the late 1890s.

Based on the font and the packaging, I think the box is from the 1930s. The guitar strings are older than the banjo strings, and I think the red packages are older than the brown. The guitar strings are packaged in a sealed square, whereas the banjo strings are in a package with a flap. The flap would have required more advanced manufacturing technology. That being said, these could be from the 1930s through the 1960s/70s.

The included strings are 3 "GUITAR A or 5th WOUND ON STEEL N744" and 1 "TENOR BANJO D OR 2ND LOOP END STEEL". Back in the day, you would have bought single strings in individual packages rather than full sets. They were cheap, but they got the job done.

I can't speak to the condition of these strings, but they are very old and probably don't sound great. I view these as collector's items more than functional accessories.