Types of Injections, Same Needle Different Depths IV, IM, SC, and ID look similar but act very differently inside the body. This visual shows where each injection goes, how deep it travels, Do You Need a Prescription for B12 Injections? OmegaQuant Does size matter? Historically, a bigger needle gauge was considered better to prevent damage to red blood cells. However, our recent guidelines recommend using smaller gauge needles (2325 G) for all Syringes and Needles Medical Syringes Luer Lock 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