Need to get a tap and clean up EGR/Air threads on header.

Measured at 7/8-18, but then I search and find that the Camaro LT1 EGR/air fittings are metric, so now I'm doubting my measurement...

Anybody know for sure what it is?

IIRC 22mm x 1.5

Apparently some later cars had 18 x 1.5 ;same thread as O2 sensor

Thanks.

That corresponds with what I found on the F-body forums - M22 for OBD1 and M18 for OBD2.

I rechecked the thread and it's definitely a -18 not a -1.5

How do you measure diameter on this sort of fitting? Not sure if it's a bolt (OD) or pipe (ID) thread...

Steve,Can you get a mike on the tube nut threads?

An 18 will measure around .670 inch on the major diameter (thread peaks) for a 1.5 thd. and .644 for a 2.5 thd.
that's roughly off a chart I saw.
Metric threads are slightly smaller than the size indicated, an 18 is 16.4 to 17.1 mm on the diameter.

Did you use a thred gage to determine that it's not 1.5?

I've onll had a couple out and never checked the threads but they sure felt like a pipe thread when I put them back together (I could be wrong though).

Quote:

~0.865" = ~22.0mm major diam.


Quote:
Yep.


And then I drove all over town until I found a place with a 7/8-18 nut to check it with...

Also after more googling found out that a lot of US cars EGR are 7/8-18. I think the F-body guys are just forcing an M22-1.5 on there. M22-1.5 and 7/8-18 are close enough that you'd probably just think it was stubborn...

Quote:

Yea, there some other metric sizes that will accept a US nut,etc.

Good Luck

Acquired a 7/8-18 oil drain plug and confirmed fitment.


For those needing a block off plug for EGR/AIR:

NAPA BK7041016


Now I just have to buy a $40 tap to fix my $150 headers.