This fitting is helpful if you have our WP319 pump or our WP333 pump for LS applications. Our standard upper hose fitting is designed specifically to seal properly, retain a thermostat inside the pump and provide for a reliable hose connection. However, the standard fitting only provides the right connection size for stock hoses. If you desire an "AN" style connection like -16 or -20 or a different size slip hose connection this adapter opens up many possibilities. It has the correct features to seal to the pump body and retain the optional thermostat but it also provides the correct female thread and O-ring bore to accept any of our "WN" style fittings.