All my life I thought they were tenderhooks. e.g. "I'm on tenderhooks", as in hooks that are fairly tender, so that's you on the cusp of pain, but not quite, as they're tender, and not sharp.
Bit I now finds out that I am quite wrong, and people are on tenterhooks.
Like, WTF is a tenter?
Tentertwo, when it's 13:50?
Or is a dweller within a small canvas structure, performing some mystical Sun Dance, dangling from the steel rods atop a gas burner sizzling their sausages?
Surely it's be a bit cold, as the temperature seeps into the hooks, and chills you to the bone?
At least if you're Abu Hamza, the fundamentalist, you can put the fun back into being mental, by dangling one handed in wardrobes, hiring yourself out as a coat hanger, and keeping all snug in wolly mammoth skin pacamacs.
The Cleric in the Cupboard - Terrorists on Tenterhooks!