The X5 Promaster Synthetic Brushes : -combine squared ferrule and 100% SRT (solid Round Taper) filament technology. The X5 brushes can be used with oil based paints but are primarily designed for use with water based coatings, eg water based gloss, acrylic eggshell, water based woodstains and varnishes to give a high quality brush stroke free finish. The R5 also has a stainless steel rust resistant ferrule.High quality professional paint & varnish brush, made with 100% SRT for improved performance.