How do we join knitwear pieces together on a linking machine?

You need to know how much Guage the knit fabric is. There are 12GG, 14GG, 7GG, 9GG, and 3GG..... flat knitting Fabrics.
It is necessary to know what type of plate sewing machine is used. Different needle types of flat machines correspond to different needle types of plate sewing machines. As normal 12GG flat knitted fabric need a 16GG sewing machine