Hi NightCabbage,

> Though does this mean that it's harder to "inset" some shapes
> than others?
> ie. the second one I made

Probably that is true (that some things will be harder than others to inset with this method), but actually in the second one you made you just should use Extrude for the second step to build the plug pieces, rather than Shell for that step.

By default extrude will make faces extrude along their own face normal, use the "Set dir" option and click 2 points vertically to make the faces extrude along the vertical direction and then you will have your plug pieces.

If you have a larger solid and you're trying to inset just one small area of it, you probably won't be able to use the method I showed here because the shell will work more on the whole object. For something like that you'll need to work at kind of a lower level, doing Offset on the edge curves, then trimming or extruding, the kinds of steps that were shown in that previous link above.

- Michael