The ZeroTech 3a ^2 Sunshade threads directly into the objective of your Zerotech 50mm riflescope. A sunshade can greatly reduce glare experienced by the shooter, especially when the sun is low on the horizon. Fits the following models: ThriveHD 2.5-15x50mm PHRII 2.5-15x50mm Illuminated PHRII 6-24x50mm PHRII 6-24x50mm Illuminated PHRII Trace 3-18x50mm R3 4.5-27x50mm R3 Trace Advanced 4.5-27x50mm RMG