It's ABS, and it floats, castors sometimes get caught on cracks and what not, figure 4 inches for every 1 gpm for width, it's not exact but real good. GPM is the guiding point not psi. GPM's give you more cleaning powerDoes the ABS cover on the general hammerhead cover a metal dome over the wand? Or is the ABS cover the actual dome? I assume the 18" creates a 16 inch path? I would think a wider path would require more PSI and/or more GPH. I think I'd rather have a faster unit with a slightly smaller path (18" cleaner) than perhaps questionable speed on a 20" cleaner. What are your thoughts? I found the 18" Hammerhead for $330 and free shipping. It is in my price range.