There is only one smasher that approaches 12 inches in length and that is Hemisquilla ensigera from Southern California. There are two other species of Hemisquilla, H. braziliiensis and H. australiensis. Both are smaller. The largest Hemisquilla I have seen was about 11 inches (28 cm) and that is plenty big. In southeast Asia the larget smasher is Odontodactylus scyllarus. The largest one I have seen was just under 20 cm, about 8 inches in length. I doubt that they get any larger than that. They are eaten, however, and I have seen plates piled high with several bright green O. s.
There are several spearers that reach or exceed 12" including several species of Lysiosquillina, Lysiosquilla, Harpiosquilla and Bathysquilla. The largest species I know of is Lysiosquillina that is reported to reach a size of around 40 cm - nearly 17 inches. The largest one I have collected was around 35 cm.
Roy