Not really sure there is any use for the 90-degree Extention, as soon as you rotate it to go under my truck it hits the ground, maybe 30 degrees would be more useful. That being said, minus the 90 it goes easily under the truck and does a thorough job, I look forward to its use. I own a 6-year-old 3100psi pressure washer, when I attempted to use it on my driveway 2 things happened, first it lifted off the ground like a rocket ship and if I forced it down the spray head are too close to the surface, and the spray heads don't come close to overlapping so you get four clean stripes on your driveway, but hey it'll clean the underneath of my truck.