Hi Jesse, even though clines make it possible to place something in the right spot in one single command, sometimes it is not worth the planning effort that it requires to get it all set up just right. Like in this instance even though it is possible to draw a cylinder in the exact spot, it is kind of easier to draw it in the orientation and then move it off ot the side as a second step.

Also I don't think that there is anything wrong with your scaffolding method, that's probably more what I would do because it kind of gives you some pretty good visualization as you are setting it up.

But anyway, to do that the cline way here is what I would do - start the cylinder command.

Drag the first cline between the tips of your stones to set up a midpoint osnap:



Now drag the second cline between the origin and the midpoint of the previous cline:



I believe this gets you your correct orientation. So now zoom in there a bit (so you can more easily snap on to just the cline instead of on to the neighboring stones), and draw your cylinder:



Now for the second step you can drag it off to the side a bit, or use Transform/Copy with a distance constraint if you know the exact distance you want it displaced from the center line.

It would have been possible to relocate that oriented line off to the side a bit first so that your cylinder would be in the exact right spot right away, but I think that may actually be more complicated overall.

- Michael