You can also use carriage bolts, or better yet, go to the hardware store's plumbing section and get ya a couple toilet flange mounting bolts. They usually come in a bubble pack and include some oval or fender type washers and some rubber washers. The good thing about using them is that they have a flat oval or rectangular head that wont protrude at all. Some are brass, some are plated steel, and some are stainless.
I've used em for all kinds of projects.