This style of needle is only suited to multi-function overlocker that do overlock, coverstitch, safety stitch.  The machine should specify EL x 705 system.  Suitable for woven fabrics
sizes 80, 90
 
EL x 705 SUK CF - suitable for knit/stretch fabrics.  This needle has a long groove on both the front and back as well as a slightly larger scarf and a medium ball point. The chrome finish (CF) reduces heat and wear and aids in slipping through the fabric.   Helps reduce skipping stitches on coverstitch.
size 80