Hi @teerawat.pSCHYQ, thanks for posting the subassembly, and sorry for not responding earlier, but I already checked the possibility of creating the shape with the looped geometry, and I found this is not possible. It turns out it is not possible to say in advance which links will enclose the shape. Therefore, the shape cannot be inserted.
A solution for this problem is to program each step of your loop manually, but you should program as many steps as you believe you'll have in your model, which is a lot. Once this is done, we can certainly know which link elements the shape will be comprised of. (I have personally done this with Slope Daylight Benches for roads, but the dimensions are greater, and I have modeled six benches maximum)
Let me ask you, what are you trying to model? Can you explain better your idea with this subassembly to see if I can provide another idea?
Best regards!
Camilo Fernández
Civil engineer | Specialist in design, construction, and maintenance of roadways