This is a Remix, but it was posted in a FB group so I can't link the original.

Original model posted by Hiddenwoods Art in an XTool F1 Ultra Facebook Group. I edited the model to fit the smaller ornaments I had.

This jig is to make it easy to engrave 2.5" glass ornaments on the XTool F1 Ultra. It secures to the plate directly in the center. In testing I have found 1.75" round designs work great. All you have to do is install it on the plate of the machine, put your design in XTool Creative Space, size it to within 1.75", center it, and engrave. 

You will want to push the top portion of the ornament back into the notch.

Engrave Settings

BL 60PWR/1800SPD/300LPI