Final answer:
Needle gauges are determined by the diameter of the lumen. The gauge of a needle refers to the size of the lumen, with smaller gauge numbers indicating larger lumen diameters and larger gauge numbers indicating smaller lumen diameters.
Step-by-step explanation:
Needle gauges are determined by the diameter of the lumen. The lumen is the hollow space inside the needle through which the liquid flows. The size of the shaft, length of the hilt, and size of the syringe may affect the overall size and design of the needle, but they do not determine the gauge. The gauge of a needle refers to the size of the lumen, with smaller gauge numbers indicating larger lumen diameters and larger gauge numbers indicating smaller lumen diameters.