Steel, sharpish, arrow-shaped things. You use them in picture framing, to hold the glass and/or the backing 'n stuff into the frame. A dollar package of glasier's points can save you $20+ in custom framer's fees.

Downside: You stick 'em in with a wide screwdriver or putty knife, and I've heard that some people have been known to accidentally stab themselves in the palm of the hand when they don't hold the screwdriver and the point correctly, and the screwdriver slips. And it hurts like a bitch. That's what I hear.