Know Your Needles A Quick Nursing Guide! Today, let's understand the different types of needles and their clinical purposes Green Needle (21G) For IM injections like Know Your Needles A Quick Nursing Guide! , Today, lets understand the different types of needles and their clinical purposes , Green Needle (21G) For IM injections like vaccines or Dr. prescribed B12 injections. Pharmacy only gave me vials. Where do you get your needles and syringes? What size?? Where do I inject? : r B12_Deficiency Is this the right size needle for im injections? : r B12_Deficiency