The OEM ford "finger trap" style nylon hose connection is often missing the retainer and o-ring. Purchasing this part from Ford costs $23, and even when complete can be hard to get a perfect seal. It is the most common vacuum leak location in the conversion, typically due to the nylon line not being perfectly round, or being routed incorrectly. This nipple replaces the ford part with a hose barb, for much easier and more positive connection. See video below for more detail. 

Made in New Hampshire