You may be right, but it is hard enough to line up the rack, fender stays and eyelet; and start the bolt without cross threading the eyelet using the correct bolt. I wouldn't take a chance on using anything but a metric threaded bolt. I think that the metric size OD is just a hair smaller than SAE. While metric recess head steel capscrews are relatively easy to find, stainless steel are harder to come by. I've used the plain steel ones and with a little care they don't cause a problem. I grease the treads, rather than use locktite, and check them regularly for snugness; which is a good idea regardless of bolt matrial.