A trivet is used to hold a pot or pan over a fire or coals. Traditionally, these would be made out of cast iron or wrought iron. But in a pinch, you can use steel shelf brackets. The materials needed are: 3 brackets, 3 bolts and 3 nuts. By bolting the tip of the long arm of the bracket to the edge of the next bracket, then repeat the positions on the next 2 brackets, you create a triangular platform. This is surprisingly stable and can be placed wherever needed. Of course you can use a warming rack or oven rack placed on bricks as a grill, but a trivet can float a pot or pan independently for more control and uses less of a footprint inside the fireplace.