Furnace Springs are are almost always coated with red oxide primer in order to avoid any potential hazards when exposed to high temperatures.
The function of a spring is to absorb movement in the pipe caused by thermal and load displacements.
In order to size a constant spring support, you must know the load and the anticipated travel. From that you can determine the amount of total travel and then refer to the constant spring support load and travel table to locate the correct size spring for your design.
Constant Spring Supports with Neoprene Coating