The way I would model the component shown on the LHS of your image is like this:
- Sketch the outer diameter of the circle on one of the home planes, say XZ, with the centre of the circle at the origin.
- Extrude the circle an equal distance in each direction, such that the XZ plane runs through it's centre
- Sketch half of a 'nub' on the same plane, with a centreline along the X axis
- Revolve the 'master nub' by 360degrees around the centreline in the sketch (coincident with the X axis)
- Use the circular pattern tool to make 4 copies of this nub, equally spaced, around the Y Axis.
The reason I suggest this approach is that it ensure that the nubs are all identical to one another, and all equally spaced and pointing radially out from the centre of the circle. IF you want to edit the form of the nubs, there's a single sketch to edit, and all other nubs will auto-update.
Using relations to control the position of things is dangerous, as they rely on the internal ID's of selected faces etc, and these are notorious for getting 'lost' as a result of model changes elsewhere in your workflow.