I got a new pocket flashlight and I wanted a lanyard for it, but it didn't have a hole for one and the base of it didn't flare enough to hold any kind of knot I knew how to tie. After I "asked the Google" I found the constrictor knot. So far I haven't had an issue with it coming loose and I've swung it around quite a bit. Here's a link to how to tie it:

http://www.animatedknots.com/constri...g.jpg&Website=