So, on Saturday I swapped my T1 4.10 with a T2 4.30, including NB subframe, control arms, and uprights. I reused all of the hardware off of my car, as some of the parts from the NB parts car were questionable. On my NA, the big diff nuts were identical to the lower inner control arm nuts. On the NB subframe, the diff nuts are a finer thread. I ran to the parts store and got some M12 x 1.25 thread, as they definitely weren't the M12 x 1.75 coarse thread. The M12 x 1.25 didn't fit either. So the thread is either M12 x 1.00 or M12 x 1.50, both freakin odd ***** that I can't find a 10.9 flange nut in. I managed to find some nuts that fit in the parts bucket, and used washers, but I'd rather put some graded nuts back in.

All of the parts guides say that the nuts should be identical, from 1990 -2005. But they're not. Does anyone have the NB part number, or at least the thread?

Addendum: Goddamnit Mazda, use common freakin bolts! It's like when I was trying to locally hunt down 10.9 M8 x 1.00 for the pressure plate bolts in the clutch....

 

Wish I could help further but have you tried going to a Mazda dealer's parts department?

You could also purchase a set of pitch gauges: McMaster-Carr

 

Mazda used very generic threads on everything but a few bolts. PP and flywheel to name a few.

Most hardware stores are to blame in my experience. They'll have 2 flanged nuts, m8 and m10, usually in the wrong cubby in a drawer no one's looked at in 10 years.

Stick with OEM, find someone parting out an NB and have them ship them to you for $5. Or buy OEM from rosenthal, but that'll probably be pretty expensive for two nuts.

 

I have a fastenal in town that had the exact size I needed when missing some odd bolt & nut sizes. Very fast and very cheap.

 

I had to go to Fastenal to get the 10.9 M8 x 1.00 bolts. They were still special order.

I have a standard and metric thread gauge set somewhere. I guess I'll pull the nuts off tomorrow and see what the right thread is and update here. I also cleaned out my storage unit, so I have the OE NB flanged nuts. Will probably sort through everything and just use the right stuff.

 

I don't think that's true, the big diff nuts are the same as the camber bolt nuts. Its been a while, but I remember mixing them up when doing my control arm bushings at the same time. you sure the thread is clean on both?

EDIT: Same part number too:
B001-39-037B

I will say, if your NA has the old eccentrics, its possible those where different. I know the NB eccentric nuts are the same thread as the NB subframe. hope that is not confusing...

 

Wasn't the same as the eccentrics. Was the same as the big lower arm bolt.

Damndest thing. I took my old nuts off of my NA, as well as my box of NB bolts, and all of the NB nuts thread on and off of the diff studs, and the NB big lower bolts. My NA nuts thread on and off of the NB lower bolts, but not the diff studs. I think my NA nuts are just trashed, or something. Weird.

Oh well, at least I have the proper flanged 10.9 nuts in there, rather than the Grade 5's with washers.

 

The fastener sizes used mainly on the Miata are JIS b1189, or Japan Industrial Standard. They're 10.9 rated, flange head and are generally a finer pitch after the sized get bigger than M6 (1.0 pitch).

 

I've seen these trashed by ham fisted people using huge breaker bars or impact wrenches to tighten these - generally in order to hold eccentric lower bushes in place.

 

The closest metric size is M12x1.25 however you're right it doesn't fit. The other closest thread sizes are;

1/2" BSF/BSW, 1/2-13 UNC or 1/2-20 UNF

All of which are a strange choice considering Mazda usually only use metric fixings.

 

.. if he hasn't figured out in the interim 5 years, I don't think he would have used an imperial fitting.