Once we convert the file to a solid body, the small triangle facets will remain on the exterior surface of the shape. Each facet is created with three points representing the vertices of the triangle, along with a perpendicular direction. In short, stereolithography, or STL files, are made up of triangular facets.Step 3 Now it's time to put the CA35 inside the extender. By the way, you could - in fact I recommend it -put the TRDC0106 on your scope already, and build the optical train as you go. Step 2 Now you insert the Visual 2' inside the TRDC0106.