I knit on the Studio/Singer/Silver-Reed knitting machines. There have been numerous models produced over the years.
The latest version of mainbed needles were placed in the MODEL 360 of the 300 series of machines. The newer 700 & 800 series have continued to use them.
The older machines with the lower numbers in the 300 series have a rigid needle and is not suitable for use with the Lace carriage. i.e. 326 model.
The newer needle for the mainbed has a CURVED spot on the underside. This shaped needle was produced to accommodate the Lace carriage which was introduced at the same time as the Model 360 punchcard machine. The electronic machine with lace carriage also used the same CURVED mainbed needle.
The Studio/Silver Reed Lace carriage transfers the stitches, side to side and needs the flexibility of the newer needle shape.