404 High-Density Adhesive Filler is an epoxy thickening additive. We developed it for maximum physical adhesive properties in hardware bonding, or anywhere that high-cyclic loads are anticipated. Blended with epoxy, it makes an excellent gap filler or structural fillets. Use this filler wherever you need an especially strong bond. You can blend it into any WEST SYSTEM 105 Resin/20X Hardener combination, G/flex Epoxy 650, or G/5 Five-Minute Adhesive.