The portion of the brush which has bristled measures 19”; include the rubber coated tip, and you get 19 1/2”; include all of that and the handle, and it is 26 1/2”.
I do not see why not. The bristles are flexible and not stiff. I found the brush easy to clean afterwards.
1 inch to 3 inches does squeeze into small areas nicely
3/8 inches just to be "safe"
Since the bristles are flexible and on the soft side, I think you definitely could. It is easy to clean afterwards too.
I ordered mine on-line with free pick-up. This brush is great.