Steel sheets are made from 1 Steel Ingot + a Fire crystal. Unlike steel ingot stacks they sell slower, but they can be a gain in gil and smithing. The Cap for Steel sheets is 36.
Crankkiller. They may be a loss if you go about buying all of your materials from the Auction House. The best way to make this particular recipe profitable is to desynth Goblin Helms and Goblin Mails for the ingots. Obtain Moghancement: Desynthesis and you get them left and right for a fraction of the cost of buying stacks of ingots.
These are a LOSS of money. Steel ingots go for 40K a stack, so even without the cost of crystals your still losing 7K per 12synths. And they sell slower.
Unfortunatly this is the only stackable synth between 30-39.