O2 Sensor bung size

[headstrong]

I've been searching the forum and needed to know the hex size and thread pitch of the rear O2 sensor for a 1995 240SX. I do not have the OEM system on my car currently and I'm installing a universal aftermarket catalytic converter. I live in FL and even though we do not have emissions testing I still want my car to have one plus want to get rid of my CEL light properly. I've already purchased the converter and will not pay more to get an "direct-fit" one. Thanks to anyone that can be of assistance in advance.BTW, I believe it is a 12mm size but not for certain.

James