Loctite 4203 instant adhesive is a thermally resistant and rubber toughened instant adhesive that cures at room temperature. This clear, low viscosity OEM assembly instant adhesive has excellent hot strength and heat aging properties. Ideal for close fitting parts. Adhesive for fiber optic components. - Loctite 4203 is a general purpose adhesive suitable for applications where heat resistance is required. It is toughened with elastomers for flexibility, impact resistance and improved resistance to heat and humidity.