Pay attention to Luker's post: They are lefty tighty, righty loosey.... opposite what you might think. It is a very unusual piece of hardware. The head is actually in the handlebar tube, and they have tapped an allen key hole into the end of the threaded shaft. (at least that is how vintage Sun Tour end shifters are configured).

Want to know how I know this? Being an idiot, I busted one by accident getting it off an old handlebar. I had no idea it would be effectively a left handed thread arrangement. I re-machined a cap screw to replace the original, and tapped the remaining center hole to make it work again. Three hours extra work because I didn't know better!