DOF for these Delevan nozzles stands for Del-O-Flo, a trademarked name type of nozzle.
"Del-O-Flo nozzles are low-capacity nozzles designed to minimize the plugging problems associated with very low flow rates. The special interior design of the DEL-O-FLO flushes contaminants through, limiting build-up. These nozzles will satisfactorily interchange with other hollow and solid cone nozzles. The Del-O-Flo is available in 0.40 GPH up to 0.85 GPH with angles from 30° to 90°."
Replied on Mar 09, 2017 by Ron from Industrial Stores