How to create recesses in a curved surface? I want to make a simple cylinder box that has a very simple twist lock. I have seen a lot of maze puzzle boxes on the net but I just want something simple. 

Ideally The lid will have 3 'L' shaped recesses in it that a lip with 3 pins in the base will key into. The lid presses down with the pins in the recess and then a twist to close.

The base would look something like this:



[Edit] I found the torus mesh. It seems like I need to play with some maths but this is kind of what I'm after, but without the continuous loop really (oh, and imagine a closed top).



Can anyone provide any good examples or links on how to do this easily.
Anything that has to be cut into a curved surface, I tend to build flat and curve into shape later. Using this method I have a model of one 'L' section and a bezier circle (origins of both objects matching each other):



Using an Array modifier with a count of '3', followed by a Subsurf set to '2' subdivisions and finally a Curve modifier:



I get this result:



Using modifiers allows you to easily manipulate the original non-curved section, while also seeing how it will look when curved into a circle.

Once you are happy, modifiers can be applied and the two ends of the circle can be merged (either by W> Remove Doubles, if the vertices are close enough, or more manual merging if they are not).

Also note that increasing the resolution of the curve on the curve's 'Data' tab will improve results. This example had a curve resolution of 30.