Our highest-quality mirror diagonals feature sophisticated, lab-tested dielectric coatings that boast an astounding 99% reflectivity. Dielectric coatings are more durable than enhanced aluminum coatings, so you'll enjoy years of exceptional performance. The machined and anodized aluminum housing features machine-threaded baffles for high contrast and a nonmarring compression ring collar for securing the eyepiece. Nosepiece barrel is threaded to accept filters. Endcaps included.