Ree:
Having the correct hex key is the secret. Also if they are rusted in place, they will be a problem as any threaded fastener will be.
I use a product called "Rust Buster" that I found at an appliance parts store that works better than W4 Diddly or Liquid Wrench in loosening stuck bolts.
PS: Their proper name is Hexagonal Socket Head Cap Screws
Jim