The Jenson Swirly Q brush is designed for scroll striping and script lettering with enamel based paints. Scroll striping requires thinner paint. If mineral spirits were to be used; the paint would run easier. I recommend using a slow drying automotive reducer for thinning enamel based paints. Clean the brush thoroughly with reducer before and after each use. Never use lacquer thinner! Always store your brush in mineral oil between uses. - Gary Jenson , Both Sizes Have The Same Diameter. However The JS-1 is 1-7/16" Out and The JS-2 is 1-11/16" Out.