Datum Question

[[Am...]]

Hi guys, I have a print that seems to have a datum referencing itself and im wondering if this is legitimate and how to go about doing this callout right.
Datum H is the minor DIA of the thread and G is the flat plane on the underside. J and K are 180° from each other. I've had issues with these prints before so id like to get a second opinion on it before I start with the program. So not only are J and K combining to create the primary datum the true positions from that are the datums. And also wouldn't you want J-K to be the tertiary datum here?

[[sh...]]

Are J and K slot features?

[[Am...]]

No they are tabs sticking out from the part.

[[sh...]]

All the info I can find is a co-axial axis are typically done on Cylindrical type features.
Typically co-axial datum construction are used for checking runout.

Even if these callouts aren't legal, I can see this still being able to be called out

[[Ma...]]

Measure a circle on -J- and one on -K- and create a 3d Line between the two. The call out refers to the centerline of J-K. Then check the features back to J-K centerline.

Mark

[[Am...]]

J and K aren't round though, its like a block. I've created symmetry points on them and recalled them into a line. And I also ran into pretty much an identical FCF online but it was a part like the one shane posted. It makes some sense in that co-axiality example but here its just weird to me, I feel like GH J-K would make a little more sense. But until I get some clarification on this from the customer im going to go ahead and use the center line created from the symmetry points.