These KF Glass Viewport Sight Glass flanges follow International Standards Organization (ISO) Quick Flange Specs. The viewport uses borosilicate glass KF NW in a one-piece assembly. This viewport replaces a blank off cap, includes a Fluorocarbon Rubber O-Ring. KF flanged vacuum fittings are commonly used to build process vacuum plumbing and systems for industrial applications. Uses KF Hinge Clamps for installation. The standard sizes are KF16, KF25, KF40, KF50. These vacuum fittings are made of aluminum 6082. For complete specs see info brochure to the left at Downloads