To calculate the correct length of cord required, multiply the inside diameter of the o-ring by pi, then add 1x cord diameter. This will then give the correct length of cord required. Using the splicing aid and a very sharp knife, make a cut in the material at a right angle. All surfaces to be glued must be free of oil or grease. Avoid touching the surfaces. A thin layer of glue should be spread over one side of the cut. A thin layer provides the best results. In order to join the two sides cleanly, use the V section on the splicing aid. Match both surfaces together and press firmly for 15 seconds. The glue must dry for 60 seconds before mounting the O-ring.