The 21104 is a replacement bit for the Shelter Tools Lutz Screwdriver, the 15-in-1 ratcheting driver Lutz makes for us. It's double-ended, with a 5/32 in slotted tip on one end and a #3 Phillips on the other.
It's the same bit that comes in the handle: 2 in long, in 6150 chrome vanadium steel heat treated to 58 to 60 Rockwell. Use it to replace a lost or worn bit; it stores in the handle with the others.
Lutz File & Tool Co. of Cincinnati, Ohio, marks its tools "Lutz since 1904." The Ragland family, who owned Lutz as a supplier of file handles, bought the Gorilla Glue brand in 1999, and the company later took the name The Gorilla Glue Company, which still makes Lutz tools.