The 4mm Plossl Eyepiece has a 1.25" chrome barrel that has been threaded to accept standard 1.25" filters, such as a neutral density filter or color filter that will help bring out features on the Moon or planets. The top of the eyepiece is fitted with a fold-down rubber eyeguard, which not only makes observing more comfortable but will keep stray light from hitting the optics and lowering contrast.