A blade includes a blade body having a surface and a hole extending through the surface of the blade body. The hole defines a hole axis and a plane perpendicular to the hole axis. The hole has an elongated hole perimeter within the plane. The hole perimeter includes a plurality of non-linear perimeter sections to minimize stress concentration around the elongated hole perimeter while maximizing the usable opening area. A rotor system includes a rotor hub and a blade as recited above. The blade extends radially outward from the rotor hub. The blade defines a root end proximate to the rotor hub, a tip end opposite the root end.