This fiber-optic sight attaches by an adhesive strip to any ventilated or solid rib or flat surface (and ported barrels) and is low profile as to not change your point of impact. The hollow tube design helps shooters use both eyes when acquiring their sight picture. It's the safest and best way to shoot. Features & Benefits- Quickly and safely acquire sight picture. Fits any ventilated, solid rib or flat surface. Can be mounted to ported barrels. Enables shooters to keep both eyes open. Ensures proper shooting form. Available in 2.5mm diameter fluorescent green and red. Available in both 2.75".