This type of needle  has a rounded tip that slips between  yarns rather than piercing them which eliminates damage in knit fabrics. Use this needle when working with coarse knits, interlock knits, such as T-shirt fabric, and other fabrics that tend to run if snagged.
Ball - point needles are the correct type  of needle to be used in Janome 3/4 thread Overlockers
 
THE NEEDLES ARE A STANDARD UNIVERSAL FIT AND WILL FIT ALL STANDARD HOME SEWING MACHINES WHICH HAVE A FLAT SIDE ON THE NEEDLE