Here's my vote for a poorly designed tool - poorly designed as in it doesn't work!
A few years ago I bought one of those Alco Products, or whatever the company name is, micro-chuck for drill bits. The end which inserts into a tool is a standard hex shank like on the phillips bits which go into a standard drill machine. The end in which the bit gets inserted is three small metal fingers encased by what looks like a brass sleeve which you screw down to compress the three fingers together to squeeze and thus hold the drill bit. The outside of the the sleeve is knurled for a better grip when turning. Nothing special here, just typical drill chuck design.
The problem is after I used it a couple times, when I unscrewed the sleeve, the fingers wouldn't "relax" their grip on the bit and I was unable to remove it. I took one of my small screwdrivers to try and gently pry one of the fingers loose, just enough to slide out the bit. Well just the slightest pressure, really, and the finger snapped right off! It looks to be some kind of cheap, cast pock metal or some such. I mentioned it to the guy I bought it from and he just shrugged and said he would mention it to his supplier. . .and that was the end of that!
Anyone else had this problem with this chuck? Just a wonderin'
Take care,
Paul "The CB&Q Guy" (Protolancing the Burlington Illiniwek River Branch in HO)