This 2" nipple is 1/4" X 1/4" NPT (National Pipe Thread) and is used for connecting regulator bodies together. We use them for Taprite, CMB and other Secondary bodies, but they can be used to connect any 1/4" X 1/4" FPT (Female Pipe Thread) parts together. These are very thick (about 170 thousands of an inch), so they have more strength than your average brass nipple which would be much thinner. They are hexed in the middle for easy attachment using a wrench.
WARNING: This product can expose you to lead, which is known to the state of California to cause cancer, birth defects and other reproductive harm. For more information go to: www.P65Warnings.ca.gov.