Edge distance
According to AC 43.13B, edge distance restrctions oblige that holes drilled are not less than 2 hole diameters from the center of the hole to the edge of the material into which the hole is drilled. Reworking the algebra, this translates to 1.5 hole diameters from hole edge to material edge. Although, while I've never heard or read this metric to be material specific, I'm currently noting violations (by dedign) in the steel of of the cleavis halves that attach my rudder cables to the pedals. Never the less, the math of AC 43.13B remains. Good luck
Hodgson
N377CP,KWVI