Schmetz Twin Stretch Needle - 2.5/70

To create 2 parallel rows of stitching, especially as a hem for knits that duplicates the look of a cover hem machine, this is one of your two choices.  The 4.0/75 Twin stretch needle has a wider space (4 mm) between the needles.  
The needles have a rounded tip as in the Stretch Needles - most suitable for knit fabrics. 
 
Londa says:  "These used to have a blue bar - but for now, thanks to blue dye being unavailable in Germany when these were manufactured during covid, they have a red bar - so be sure to put them back into the package so that you know they are the Stretch variety - for knits, instead of Universal as also has the red bar." 

Londa says:  "Be sure to stabilize with stretch interfacing on the Hem ALLOWANCE and to lower your needle tension a bit to create a non-tunneled, nice look on your knit hems.  
See my knit DVD for many hints on stitching with twin needles:  Stretching Your Knit Sewing Know-How.