Oh...almost forgot!! That thing Les was referring to is called a "bone folder"...now, before you get all nasty here, it's called that because it is used to crease heavy paper to assist folding it...and it was made out of animal bone a long time ago when animals had bones & you could use them for stuff.
You can find bone folders at arts & crafts stores usually in the stamping and scrapbooking sections.

Jeanette