Singer 4423 HEAVY DUTY Electric Sewing Machine This SINGER HEAVY DUTYsewing machine is a true workhorse. With a heavy duty metal interior frame, stainless steel bedplate, extra-high sewing speed and powerful motor, it can sew through just about anything you throw at it. Convenience features including an automatic needle threader, top drop-in bobbin, fully automatic 1-step buttonhole and drop feed for free motion sewing adds a new dimension of ease to heavy duty sewing.