These are two layers, Inlay within an Inlay is backed by a second shell. The total thickness is 0.060" so each layer is about 0.030".
Be sure to inlay it deep enough so you don't sand through the design.
You can just route a circle and drop them into place.
These are sized to match the sizes of American Fostner bits so you can also place the part to be inlaid on your drill press and set the depth to 0.060" (1.5mm).
nlays come to you attached to cardboard with a water based glue (Like Elmers School Glue) to be easy to remove by soaking in warm or hot water.
The boards are also shrink wrapped to be sure that if any section should come to you loose in the package during shipping they will remain within the shrink wrap.