Pump inlet strainers (a.k.a. filter, "rock catcher") helps prevent debris from being suctioned into the pump, which can cause damage to your sprayer.
Reducing adapter is for early 190ES Hi-Boy models and 190ES stand models.
For Use with these airless sprayers:
Pump inlet strainers are common parts for all airless sprayers. Many inlet strainers are compatible with sprayers that are not listed above. Consult your parts manual to ensure the correct strainer is purchased.