[josh stout]

I once asked Scott Rodell about the brass spring loaded wrist darts from China that one occasionally sees on eBay, and he said that, while he was skeptical about the ones for sale, they were based on a real weapon. Chinese throwing knives, needles etc. are pretty rare, though they are well documented in martial arts styles and period novels. The wrist dart holders look like brass tubes around eight inches long and shoot needles like short fat knitting needles. The dart is spring loaded. There is a groove going around near the tip of the dart and this slots into a small release mechanism that can be depressed with a finger.

I can't think of any similar arrangement where a fixed blade sprang out like that. There were double and single knives or even small maces that were traditionally hidden up a sleeve, but nothing fixed. The Chinese like to be able to spin their knives around.
Josh