Gussets can be considered as a subset of ribs and the guidelines that apply to ribs are also valid for gussets. This type of support is used to reinforce corners, side walls, and bosses.
Guidelines for gussets.
The height of the gusset can be up to 95% of the height of the boss or rib it is attached to. Depending on the height of the rib being supported gussets may be more than 4 times the nominal wall thickness. Gusset base length is typically twice the nominal wall thickness. These values optimize the effectiveness of the gusset and the ease of molding and ejecting the part.