Model 34590-50 is designed to comply with the Pennsylvania modified Babcock as referenced in APHA 15.8. Models 34590-55,-56,-60, and -61 include a special rubber washer that allows air displaced by incoming milk to escape freely. Models 34590-55 and -56 meet ASTM Specification E1043, Type II A requirements; models 34590-60 and -61 meet ASTM Specification E1043, Type II B requirements. All pipettes feature permanent brown-stain scales.