Long thin sections in a design are hard to fill.[1] Sudden changes in wall thickness reduce castability because it induces turbulence during filling; fillets should be added to avoid this. Annulars in the path of flow should be avoided because they can cause cold shuts or misruns. A design that causes isolated hot spots decreases castability.[2] An ideal design would have progressive directional solidification from the thinnest section to the thickest.[4]