APERTURE system variable
Entity snap aperture
Specifies the size (in pixels) of the entity snap aperture box. Values between 1 and 50 are accepted. The program searches the area inside the rectangular aperture cursor for geometric features, such as endpoints and mid points. A large aperture cursor makes it easier for you to hover over geometric features, but then the program may find too many matching entity snap points; a smaller one may be more difficult for you to position over geometry, but is more precise at snapping to geometric features.