"Perfect for gutters"
These work great for rain gutters or thin tiles. I was hoping they would work on the thicker (1") roof tiles on my house, but they wouldn't open up that wide.
To use them on a rain gutter, you twist one of the pieces off to detach it, and then you snap the post into the smaller hole. The larger piece clips into the gutter and the smaller piece holds the light. You can twist that up and down to adjust the orientation of the light.
TIP: Don't wait until you plan to use these before you assemble them. It takes a little time, so you should plan to sit in front of the TV and put them all together the night before.