Disclaimer: I'm not advocating brass over copper or vice versa!
For those who prefer thick Brass washers and don't wish to stack em', the ones I just received from McMaster Carr appear to be good alternatives to the MikesXS product (#01-0651) from both a specification and cost standpoint.
They come in packs of 5. $9.42/pack.
PN:
95395A240, OD: 7/8", ID: 13/32", Thickness: 0.11" - 0.14"
With $6.25 shipping to east TN, I paid a total of
$25.09 for 2 packs (10) of these.
If you order 8 (yes, you may only need 4 for outer studs!) from MikesXS, this will cost you $23.60. UPS Shipping these to east TN costs $14.39 for a total of
$37.99.
The McMaster Carr brass washers (fit nicely around 10mm threads).
I measured 5 of McMaster Carr brass washers (w/Mitutoyo Digital Caliper):
OD: 22.13 mm
ID: 10.32 mm
Thickness: 3.21 mm
I have never ordered MikesXS brass washers. I just installed an 8-pack of Suzuki Copper Washers (#09168-10017) atop one of my C's cylinder head. Plan to install these brass ones on my other C. The Suzuki's torqued to 30 ft-lbs. just fine. They measured at ~2.4 mm thickness as I recall (going off of memory).
Gee, there's a bunch of threads on this topic! None that mention the McMaster Carr option to my knowledge.....
http://www.xs650.com/forum/showthread.php?t=24086&highlight=brass+sealing+washers