Similar to the bones of your spine protecting the spinal cord, casing is tubing that is set inside the drilled well to protect and support the wellstream. In addition to providing stabilization ...

That'll give you a 3/16-in. reveal. Place the top piece and hold the trim 3/16 in. away from the jamb at both ends and along the base of the window casing. Nail the trim to the jamb with 1-in.