s4 n/a exhaust bolt sizes
 

I couldn't find these anywhere so I just went under my car with dial calipers. I figured other people might also want to know because these bolts often rust and need to be replaced. Mods: Feel free to archive, edit, splice into existing archives, or do whatever else you want with this info.

NOTES:
1. I'm confused about why I found 2 pre-cats because I thought s4's only had 1. Maybe 1 isn't a pre-cat?
2. I measured all the thread spacings to be 1.00; that's obviously wrong for the M10's and M12's, so I put a "?" on the M8's (1.00 or 1.25). I would guess fine thread (1.00), like the rest.
3. I think the bolt heads are 10mm thick. So you can subtract 10 from the lengths below when shopping.
4. "O2 Sensor" and below are copied from the archives.
5. While my exhaust is horribly rusted, my exhaust hanger bracket bolts, suspension fasteners, sway bar fasteners and drivetrain fasteners had no rust.
6. Use only high strength automotive bolts.


Exhaust

Mufflers to Y pipe (4 bolts & 4 nuts): M10 x 1.25, 50 mm long including head, 14mm head
main cat and both pre-cats to eachother & y-pipe (8 nuts): M12 x 1.25, 17mm head
air tube to main cat (2 nuts & 2 bolts): M8 x ?, 35 mm long including head, 12mm head
other bolts on main cat (2): M8 x ?, 25mm long including head, 12mm head
brackets that connect exhaust hangers to chasis (4 bolts): 12mm head
oval exhaust hangers (2 nuts): M8 x ?, 12 mm head
donut exhaust hangers (4, no fasteners)
O2 Sensor: M18 x 1.50
Exhaust Manifold Flange Where the pre-cats attach: M12 x 1.25
Racing Beat Presilencer: M12 x 1.75
N/A Exhaust Manifold: M10 x 1.25
TII Exhaust Manifold Nut: 10mm x 1.5

To my unterstanding, the studs (cat) are 1.25x12mm w/ 17mm nut heads. Of course, I have an S5, but I don't see why that would differ from S4 to S5.

I wrote "I would guess fine thread (1.00) like the rest" when all the other bolts are 1.25. IIRC 1.25 is fine thread for M10 and M12 but 1.00 is fine thread for M8 and 1.25 is coarse thread for M8.

1RevvinFC3S: Yeah those are the same numbers I got for those nuts on my s4.