sight size

daylight width, sight size, sight width

The width of a glazed opening which admits light.

sight size

In a window opening, the actual size of the opening that admits light.
References in periodicals archive ?
Caption: Choose a peep sight size that appears just slightly larger than your sight housing at full draw.
36031 to a "sight size" matching that outside diameter (in this case, 8 15/16 by 17 1/16 inches.