APHA Nessler tubes in matched sets of 6. Shadowless bottom transmits undistorted light. There are no dark spots when the tube is filled with liquid and viewed from the top using a light source beneath the tube. Narrower and taller with a much longer scale length than 45310. The 50 mL size is specifically mentioned by the American Public Health Association in Standard Methods for the Examination of Water and Waste Water (Method 4500-NH). Rings and legend are durable white ceramic enamel. Rings coincide with specific volumes of liquid. Designed from Federal Specification NNN-T-175, Type 1, Class 2 requirements. Supplied in a matched set of 6. Graduated ring scaleof any of the tubes will not vary by more than 1.5 mm for the 50 mL from that of any other tube within the set. Graduations: at 50mL. Dimensions (O.D. x L): 20mm x 300mm. Scale Length: 200mm-220mm. 6/Set; 1 Set/Case. Kimble® #: 45315A-50.