The Kester 44 rosin flux is an activated rosin formula for use in flux-cored solder wire. 44 has virtually dominated the field of activated rosin core solders for well over four decades. 44 is classified as ROM1 per J-STD-004. - An outstanding performance feature of this flux is the 'instant-action' wetting behavior. The high mobility and fast-spreading action of this flux results in more reliable production line soldering.