I was always told 1.5 x the diameter for engagement, 1/2" equals .75 of engagement. Specifically with todays quality of parts.
This will help overcome soft material, smaller thread engagement, ect.
Thread engagement distance calculation thumb rule
In case of the threads for steel – Min. thread engagement distance = 1.5 x base diameter of screw or bolt
In case of the threads for cast iron, brass – Min. thread engagement distance = 2 x base diameter of screw or bolt
This will help overcome soft material, smaller thread engagement, ect.
Thread engagement distance calculation thumb rule
In case of the threads for steel – Min. thread engagement distance = 1.5 x base diameter of screw or bolt
In case of the threads for cast iron, brass – Min. thread engagement distance = 2 x base diameter of screw or bolt