Definite knock off. Diamond/Duluth made these in two sizes - DH-18 is the larger size. DH-16 is the smaller one.
I believe the patent was licensed to several other companies or the tools were contracted from DD. Either way you find a lot of different brands on similar tools from the same era. The Chinese version isn't as nice, but it is functional.
"It didn't hurt, flirt, blood squirt, stuffed shirt, hang me on a tree
After I count down three rounds, in Hell I'll be in good company" - The Dead South