Luxo STAYS (Self-Traction Accessory Yield System) Lenses are for use with KFM, KFM LED, WAVE LED, LFM LED and Circus Magnifiers. Simply moisten the silicon gasket around the lens and gently press down to affix the STAYS lens to the magnifier primary lens. The lens itself has a 2" diameter (2.5" including the silicon gasket frame). 4-Diopter STAYS Lens: When used with a 3D/3.5D lens the working distance is 6". When used with a 5D lens the working distance is 4".