This is OptiSIGHT™ optional lens plate #7 which provides 2.75X at a 6" focal distance. 

The makers of the world renown OptiVISOR® are proud to offer their lightest weight product: OptiSIGHT™. 

This very lightweight, yet very tough magnifier features a visor assembly with pivot mechanism and headband with adjustable strap for comfortable extended wear.  Precision optical grade acrylic prismatic lenses. Provides handsfree magnification. Brings work into focus, reducing eye strain and fatigue.   Visor can easily be worn over prescription or safety glasses. Made in USA