OTC's 6750 Diesel Fuel Hydrometer allows technicians to quickly troubleshoot engine performance problems and measure #1 and #2 grade diesel fuel quality. Hydrometer measurements are given as an American Petroleum Institute (API) gravity reading when testing diesel fuel composition and combustion characteristics. Fuel is drawn into the hydrometer tube which then floats the internal bulb float, The internal float contains a thermometer that is used to compensate the API reading for the highest accuracy. Hydrometer Scale: 30 to 110; Correction Scale: +2.5 to -5.0. Applications include #1 and #2 grade diesel fuels. Similar to OE tool number J-38641-D. Instructions included. Value is at the core of the OTC tool and equipment portfolio. For a simple repair or the most complex drivability concern, these award-winning tools universally solve problems faster, and at better value, than any other product line available. Whether it's a specialty tool or unique piece of service equipment, OTC provides top solutions to modern automotive service challenges while increasing technicians' productivity and shop profits.