Pipe tap problem IV 2010 Pro

[retiredoldflattus]

I have a cast iron hemisphere and I want to put a pipe tap in the bottom (from the outside). It has a wall thickness of 1" so I drilled a 1/4" hole thru and then counterbored 1" dia. x 1/2" deep and then tried to put a 1/4" pipe tap at the bottom of the c'bore figuring that a pipe tap into that thick a wall wouldn't work. Well, it doesn't work anyway. When pulling down the thread list, NPT is not listed although the DIN and ISO pipe threads are. BTW, the tap is for a Parker drain cock.

 

[retiredoldflattus]

Never mind. I specified a straight thread when what I needed was a tapered one. Brain fart