If you have corner forces turned on in your model, HyperSizer uses the maximum corner force for each edge along the joint boundary. If you do not have corner forces turned on, then it uses just the average element force applied to each edge of the joint. So the forces come from element forces (i.e. Nx, Ny) and not from nodal forces divided by length.

It does not use the Nx, Ny directly as it comes out of the F06 file, rather it transforms the forces into “joint” coordinates. So at each edge along the joint, it takes the element Nx, Ny, Nxy and transforms it into a joint Nx, Ny, Nxy where the x direction is parallel to the edge, the y direction is perpendicular to the edge. Then these are the forces that are fed into the margin of safety calculation. For the pulloff margin, it takes the Ny edge force and compares it to the tensile pulloff allowable (or if Ny < 0, uses the compressive pulloff allowable). For the shear margin, it compares the edge Nxy force to the joint shear allowable.