Use a ruler or a micrometer and give me all of the dimensions of the gasket you need. For instance, a back plate gasket will have an inside dimension for the circle, an outside dimension, and usually four holes for the screws that hold the back plate on. Give me screw hole sizes and distance from the center of one screw hole to the other, across the middle of the circle. For an exhaust port, give me the size of the port, the size of the exhaust boss, and the size and hole spacing center to center. (HINT: You don’t have to measure from the center to the center. It’s easier to measure from the left edge of one hole to the left edge of the other hole, for the same result.)
I will also need to know what kind of paper you want it cut from. I don’t cut synthetic materials because I don’t want to stink up my shop. But you can have office paper, manila folder, or thicker card stock from food packaging.
Back plate gaskets are needed to prevent air leaks, of course. Exhaust gaskets can be useful for keeping oil from seeping out of the joint, and they can act as a spacer to put more distance between the muffler and the fuselage, as shown in the photos below.