High quality 1.5" acrylic dome, with 1/4" flange. Great for many uses. Could be used as a pet window in a gate, a kid window in a playground, a cover to protect a surveillance camera (may possibly interfere with motion detection), a cover to protect an all-sky camera, a cover for a skylight (if sealed sufficiently), and anything else you can think of. Note that the shape is half a sphere and that two put together could make a nearly perfect whole sphere.