This model represents the World War Two-era N-3C gunsight with North American Aviation sight head. From about 1943, this gunsight was fit to many Army Air Force aircraft including the P-51B, P-51C Mustang and P-40 Warhawk.
From aircraft-gunsights.com: "The N-3 series of gunsights was by far the most produced and definitely the most widely used AAF gunsight of WWII as it was, at one time or another, fitted to almost every AAF fighter, attack plane, medium and light bomber, but also trainer and even observation plane that needed a fixed gunsight. It was also used briefly as a turret sight at least on B-24’s and probably on Martin top turrets."
This model does not include the glass reflector plate of the real gunsight.
This model was designed by Peter Castle.
Model © Peter Castle. This model is offered from Model Monkey by permission. This 3D-printed item may not be copied or recast.