G & H Barnett Black Diamond File works.

G & H Barnett of Philadelphia used the brand name Black Diamond File Works starting the business in 1863. 

Nicholson bought Barnett in 1912 and kept Black Diamond as a file brand name.The Nicholson Brand is now owned by Apex Tool Co. and from what I see online, the files are now made in Mexico.

Iron Age Mar 07 1895