We have been using Comet rotary nozzles for the last few years. They have been serving us preaty well. Suggest that you get the smaller (physical size) nozzle. These run faster(rpm)seem to clean better. The larger(physical size) don't seem to come into there own until you get over 5000 psi.
You should use the same size rotary nozzle as you use on your machine on a regular basis. My chart shows that a 3500 psi machine should use a 5.5 nozzle to deliver 5.2 gpm.
We have been paying around $50 for these nozzles.
Dave Olson
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Tidy Powerwash Service, Inc. P.O. Box 781, Catlin, Illinois 61817 Phone 217-427-5557, Fax 217-427-2632 We are a commercial cleaning contractor serving East-Central Illinois and West Central Indiana since 1984.
http://www.tps-inc.com/preswash.htm