A flat rubber gasket can be cut from a vector file without a separate cutting die. The file defines contours and holes. Successful sealing also depends on the rubber, mating surfaces and operating conditions.
Start with the connection
Use the dimensions of the actual flange or enclosure. Locate the inner opening, outer edge and bolt holes from the same reference points. Consider more than bolt fit: enough material must remain around holes and along the sealing edge.
A photo can help describe the shape, but without a checked scale it is not an accurate production drawing.
Choose rubber for the operating conditions
Temperature, fluids, movement and compression determine the properties required. Silicone, solid rubber and foam rubber are not automatically interchangeable. Compare actual products in the rubber collection.
Oil, food or chemical contact requires product-specific information. A general material name does not establish suitability.
Do not force the gasket into place
A hole that only fits when the rubber is heavily stretched may move or locally thin the gasket. Use holes and contours that fit the connection. Thickness must suit the available space and desired compression.
Try it on the actual components
Make one gasket and check location, holes and edge width on the real connection. Then test its function in the intended conditions. For geometric fits, read about designing holes and slots.