AARG! Haltech Oxy sensor
 

darn the oxygen sensor that came with the Kit
will not screw into the RB 3" DP!

MY whole exhaust is one Piece!

what size is the Haltec sensor and the STock Mazda one??

Thats strange I have the RB 3in DP and the haltech 4 wire sensor threaded in perfectly. I thought all O2 sensors had the same thread.

Yeah they are all the same size, I would try a thread chaser in the bung , could be some thread from the old sensor stuck in the bung..Max

AFTER ALOT! of tries and wd40 it finnaly screwed in!

My car is "almost" ready for her first fire up.....

Yeah I didnt have any problems with my RB DP and 4 wire haltech. Anyways, the thread pattern is 18mmx1.5mm