bolt anti-corrosion coating
 

Anyone know what type of coating this is on the caliper bolt? It almost looks like brown-ish gold paint but it is not paint. Its not yellow zinc or cad either. I have seen a lot of different types of coatings over the years but haven't seen this before. After 47k miles, the bolts had nearly no corrosion on them and were easily removed without issue.

The new bolts from Porsche came in black oxide. I elected to go with SS studs from Tarret since I didn't like black oxide.

Maybe some sort of chromate. (which is over zinc IIRC?) You can get TONS of different shades of colors even by the same process. Its hard to rule out anything w/o a chemical analysis.

Its called cadmium II plating.

Thanks Matt. I now know what to ask when calling to check stock at dealers. I wish the replacement bolts provided would have had the same coating as the originals. I would have used them in a heartbeat in lieu of $125 for the studs.

Cadmium is real nasty stuff and is not used as often as in the past.

Update: I really wanted to stay with stock bolts and ended up contacting a dozen or so dealers. They all only had the black oxide bolts. However, the Tarret bits ended up being a nice upgrade.

The shoulder at the base of the stud is nice, ensures a good shear connection. I'm looking at GT3 studs that don't have the wide base and rely on the nut to center and capture the caliper, I worry that this allows a little bending moment on the bolt (on top of the shear force at the base). :?

How does that change the shear force?

A bending moment plus a shear force causes a weakened area at the edge of the shear where the moment creates a tensile stress. Better yet: tensile stress plus shear stress is worse than shear stress alone. Think Von Mises.

I'm trying to understand why Porsche set up their caliper studs that way, it's SOP on all the Cup cars. I assume that the bending load is insignificant compared to what they gain by having the stud slightly downsized - but what is that gain? For reference, my caliper bolts (which fit tightly through the caliper hole with zero slop) are 12 mm in diameter whereas the GT3 studs are 10 mm in diameter.

I’ve been contemplating a move to caliper studs to avoid frequent bolt removal/replacement. However, looking at the stud pictured, it won’t work for my situation due to the 14mm spacers used to position my calipers outward on the larger than stock girodisc rotors. In effect, the shoulder on the stud would “capture” the spacer, but not the caliper.

Anyone know of studs that provide a snug fit to the caliper holes similar to the stock caliper bolts as Jay mentions?