B H , I'm pretty sure before 70's. I used to think the area was mined in the 30's, based on some records while researching the property but now I'm thinking maybe as recently as the 50's. The bit has threads and just one hole on top. Googled images and it is old but can't narrow down a decade. Thanks for the help I'll keep looking. P.S. not that the 50's are old.