I just cut off a section from the Sally's coil and then cut it in half lengthwise for a 2.5mm coil. I save the other half for next time. I roll the new wick between my fingers to compress it and then twist the end to make it fit into the coil. Pull it through while twisting and then cut the tails to equal the coil diameter. Thoroughly saturate the wick with juice until it's full and put the atty back together. The wick always feels a little too tight, but rayon shrinks. When I change my rayon wick it's not nearly as tight as it was when installed. Usually, I can just pull the old wick out of the coil without twisting. Once in a while I use a Kho Gen Do wick for comparison, but I always to back to Rayon. Rayon after a week is still working fine. Cotton needs a change every few days.