With the great exchange rate between the US and the UK, I recently scored a set of Keizer Formula Kosmo wheels with magnesium centers for my Fiat on eBay.co.uk. Came in at roughly half the price of new. They're 13" x 6".
The wheels look like they have never actually been used - the bolt seats showed no galling or anything. But they came with these goofy purple bolts.
I was all set to just run them until I got my tires mounted up and one wouldn't hold air. The rim halves needed to be resealed. I stripped the wheel down so I could replace the sealant, and discovered that those goofy purple bolts weren't painted purple. They are purple anodized. Yeah, and I'm reasonably certain by the color of the metal that they aren't titanium either. Aluminum socket head bolts. M8 x 1.25. The ends were trimmed to length, but they did a decent job as I can see that the work was done on a lathe. All disassembled:
So I went back to the original auction and noticed that one of the potato cam photos from the original seller showed the centers unbolted. So now I'm assuming that the bolts were replaced with these lightweight items.
Bolts are in good shape, but I'm leery of trusting these fasteners in a street car, even if it is just a 2k lb X1/9. The wheels are super light as it stands now, and I don't have any qualms about adding a little weight by going with a steel or stainless fastener.
What says the hive? Are aluminum socket head cap screws commonly used in lightweight wheel assembly?
No idea of answer to your question, but those are sweet wheels!
Black Forest Industries sells BBS parts, and their bolts are stainless steel or plated steel.
Looks like a good excuse to add Titanium!
There are enough of them that even cheese grade aluminum is probably overkill. It'd still bother me though and a handful of black steel M8 socket head screws are cheap and don't weight much.
But will you get corrosion if you use steel bolts?
When I rebuilt a set of Epsilon-Southern Ways wheels a few years ago, I ran into trouble sourcing the hardware. Needed cap-head bolts with a weird size and shape.
I brought a handful of the original bolts and nuts to Mutual Screw and Tape in north Jersey. They were able to find the right size and load rating, plus they gave me multiple options for finish and weight. Price was cheap, too.
Those are pretty big for the loads those see. I've got a couple sets of Kodiak 13" 3-piece wheels for my SCCA P2 sports racer which use 1/4-28 socket flatheads (which install from the rear) with tiny 12-point "jet nuts" on the front. Even the BMW/BBS Style 5s on my e39 wagon only use M7 fasteners.
Thanks for the input everyone - I've ordered new fasteners from McMaster-Carr. M8 1.25 is common, so I had lots to choose from.
That said, I went ahead and reassembled the wheel with the existing hardware. I'm headed back up to Canada for another work trip this week, and there is a legit drifto shop not far from my office in Vancouver that does mount and balance far, far cheaper than I can get here in the states. I'll get this tire mounted and balanced up while I'm there, then swap fasteners one at a time when they come in.
For what it is worth, the aluminum bolts torqued to 13 ft lbs without failing, which I'm a little surprised about.
Will my dynamic balance be off by swapping to heavier bolts? Probably, but I'll see how it goes before committing to another round of balancing.
I went ahead and weighed the center just for fun: 1 lb, 5 Oz. They're under 6 lbs per wheel as is with the fancy hardware. Light enough to make me a little nervous.
Just cause they're al doesn't mean they're weak, 7075 is strong e36m3.
the wheels come apart so that you can literally assemble it inside of a tire, and you are going to pay someone to mount the tires???
In reply to novaderrik:
Slow down there turbo. 
I reassembled with the tire mounted. I just need to get it balanced. When I said mount and balance above, I meant they still need to seat the bead. 
