an inner needle assembly, comprising a first plug-in portion plugged in with a fastener, wherein the first plug-in portion comprises two first outer limiting walls arranged in parallel and a first limiting plate located between the two first outer limiting walls, and the first limiting plate is provided with a first protrusion;

an outer needle assembly, comprising a second plug-in portion plugged in with the fastener, wherein the second plug-in portion comprises two second outer limiting walls arranged in parallel and a second limiting plate located between the two second outer limiting walls, and the second limiting plate is provided with a second protrusion; and

the fastener, comprising a third plug-in portion plugged in with the first plug-in portion, and a fourth plug-in portion plugged in with the second plug-in portion, wherein the third plug-in portion comprises two first inner limiting walls that have a T-shaped longitudinal section and that align with the first outer limiting walls, and a third limiting plate arranged between the two first inner limiting walls and aligning with the first limiting plate, wherein the third limiting plate is provided with a first groove mating with the first protrusion; and the fourth plug-in portion comprises two second inner limiting walls that have a T-shaped longitudinal section and that align with the second outer limiting walls, and a fourth limiting plate arranged between the second inner limiting walls and aligning with the second limiting plate, wherein the fourth limiting plate is provided with a second groove mating with the second protrusion.