im replacing my o2 sensors in my b16 crx and was wondering for what model do i order them? and is there a difference between the primary and secondary?

 

Yes, there is a difference, primarily in the plug. One of the O2 sensors you will not be able to find a replacement for. What you'll have to do is order two O2 sensors for a CRX Si and then rewire the plug that you added when you installed the B16A so it has a CRX-style O2 sensor plug.