FLUX Pen Water Soluble 2331ZX 1/3oz. Kester Flux-Pen is a unique tool for rework and touch-up soldering. It allows controlled application of flux, eliminating the mess from flux bottles. The chisel point allows for work in very confined spaces. The flux pen is ideally suited for tab assembly no-clean and surface mount rework application because it can deliver flux to a specific area. Kester 2331-ZX Flux Pen is designed for leaded and lead-free rework of conventional and surface mount circuit board assemblies. Kester 2331-ZX is an innovation in organic acid water-soluble flux chemistry for soldering circuit board assemblies. This unique, neutral pH chemistry flux provides the best ionic cleanliness of any organic water- soluble flux available to the electronics industry.