Sinkers are small metal plates that reside between adjacent needles on the bed. Their primarily purpose is to provide takedown—downward pull on the fabric that is attached to the machine. A sinker provides takedown by extending outward and holding down the loopa that rests on the needles above it. Not all machines have sinkers, but they are found on Shima Seiki SWGN2 machines, among others. They are not found on machines like the Kniterate, which instead uses rollers for takedown.
Sinkers come in very handy during short rowing.