Final answer:
In single-line piping drawings, flanges are often depicted with a double line to indicate where pipes are bolted together for easy disassembly. Other items like pipe supports, elbows, and gaskets typically do not receive such emphasis in these drawings.
Step-by-step explanation:
When piping is drawn in a single line, certain items may be represented with a double line for clarity and emphasis. The item that is typically shown with a double line when a single line is used to represent piping is a) Flanges. In engineering drawings, especially in the field of mechanical and piping engineering, flanges are often depicted this way to indicate where two sections of pipe are bolted together for disassembly without cutting the pipe. This allows for easy access for inspection, cleaning, or modification of the piping system. Other items such as pipe supports, elbows, and gaskets are not usually depicted with a double line in single-line drawings.