Needle Sizes Explained: Choosing the Right Gauge for Different Injections Choosing wisely: needle length and gauge considerations for intramuscular and subcutaneous injections Not all shots are the same here's a guide Injections are a fast, effective way to deliver medications, nutrients, and vaccines directly into the bodybut not all injections are the 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,