Type B or solid nozzles produce a spray that distributes droplets fairly uniformly throughout the complete pattern. The spray pattern becomes progressively hollower at higher flow rates. Solid nozzles provide smooth ignition and efficient combustion, particularly in larger burners. The first number (. 50 – 1. 75) represents the gallons of oil per hour pumped through. Then the second number represents the degree of the angle at which the oil is sprayed. The nozzle on an oil system should be changed every other year.