Bought this in an antique mall this morning, Jacobs 16N 1/8"~5/8" capacity. Instead of the usual morse taper shank sticking out the back there was a 1/2-20 threaded rod in an adapter. I figured I'd pull the shaft out and free up the internal jacobs taper to mount on a lathe. Much to my surprise there was no jacobs taper, just a very odd .970"-14 internal thread. I downloaded the Jacobs catalog and it isn't listed so it must've been a custom for a specific machine...
Here's An Odd Drill Chuck For You...
Here's An Odd Drill Chuck For You...