5500-X8 Brass ConeJet Adjustable Spray Tip.
Knurled body of tip rotates through a half turn to provide spray selection from wide angle, finely atomized cone spray to a straight stream spray. Tip settings "A" and "B" represent two extreme points of rotation in tip adjustment. Other sizes available.
This is a very functional spray tip, easy to adjust to give good coverage at many different distances.