King Nipples

https://www.pipenipples.com/king-nipples/

A King hose nipple fitting is a type of plumbing or piping fitting that is used to connect two sections of threaded pipes or hoses together. The King nipple pipe connector has a male threaded end on one side and a smaller diameter, unthreaded section in the middle, followed by another male threaded end on the other side. The unthreaded section in the middle is often referred to as the "nipple" and is typically used to provide additional support or reinforcement to the joint.