Fillet radii are extremely important but are often overlooked by component designers.
 

• To avoid high stress concentrations in the component and the die, fillet radii of the appropriate size must be used in all internal and external component edges
• The exception to this rule is where the feature lands on the parting line of the tool
• An important aspect of fillet radii is that it assists in filling the part die
• There is an optimum size of fillet where structural parts are concerned
• Although increasing the fillet radii size will generally decrease the stress concentration at the bottom of a rib, eventually the mass of material added by the fillet will induce shrinkage porosity in that area
• Designers should also note that fillets applied perpendicular to the parting line of the tool require draft
   

Designs that are less desirable and should be avoided