Sponge bars, needle retainers and substitutes:
Most knitting machines have some mechanism to keep the needles firmly in their channels under just enough pressure to perform predictable. A strip of sponge supported on a metal tray is the most common modern mechanism but strips of felt or leather and brake springs are also found, especially in vintage machines. When the needle retaining feature suffers wear and tear, random misbehavior may start to occur. It can take the form of mis-patterning,  randomly skipped stitches and carriage jams. This playlist covers many needle retaining methods and what to do to return a machine to peak performance even if you can't get an exact replacement for the original item.