This adapter allows you to fit the new style threaded jet inserts into the old style (push in) 3 and 4 jet bodies. You will be required to remove the old push in style adapter from the old jet body and fit the new style adapter.
Sold Individually, not in pairs like the photos.
If these are out of stock, you can buy the similarly-priced bodies and remove the inserts to use in the old jet body.