The Fireye 46-58 1/2" Quartz Lens UN Fitting is a high quality protective lens designed for use in flame detection systems in the HVAC systems. This is 1/2 inch long, protecting sensitive components that sense flame from dirt, heat, and moisture to give you optimal performance. https://www.partshnc.com/46-58-fireye-quartz-lens-for-60-129012-un