The Self-Barlow attachment is a disc with a white screen on the front and a small built-in Barlow lens in the center of the disc. It is then screwed into the Howie Glatter laser collimator (sold separately) aperture and provides a highly compact method for Barlow-collimating.
Square Grid Projection Attachment: A 10 x 10 line square grid pattern. It spreads 21 degrees which allow centering of optics as fast as f/ 2.7.
This pattern is recommended for general use because it can be used with the fastest telescopes likely to be encountered.