Well-suited to applications not requiring a micrometer. Alignment telescopes are made of heavy walled, heat treated, alloy steel tubing meeting AIA specifications. Length: 14″. Available in magnification 20x at 2 inches, 30x at infinity. Effective aperture: 1.34″. Resolution: 3.9 arc seconds. Also available in WK-51-1100, which has a 6.978″ barrel. The outside diameter is 1.7494 to 1.7497″. Length: 9.5″. Magnification 20x at 2 inches, 30x at infinity. Effective aperture: 0.925″. Resolution: 6.0 arc seconds.