Which of the following needle gauge sizes has the largest bore (opening)?

The 18 gauge needle has the largest bore, which allows for greater flow rates of fluids compared to needles of smaller gauge sizes. Needle gauge is inversely related to the bore size; as the gauge number decreases, the diameter of the needle increases. Therefore, an 18 gauge needle has a wider opening than a 20 gauge, 22 gauge, or 25 gauge needle. In practical applications, the larger bore of the 18 gauge needle is beneficial for procedures that require the rapid administration of fluids or for drawing blood, as it reduces the time necessary to deliver or extract the required volume. Understanding needle gauges is essential in clinical settings to ensure correct choice based on the specific needs of the patient and the procedure being performed.