1/4" Vee Jet Strainer/Valve Check H45
It requires 2 psi to push the spring move the ball away to allow the water to flow. This helps make carpet cleaning wand dripless on the dry stroke.
If this is for a carpet cleaning wand, you would want them.
Please make sure your wand has enough clearance on the inside of the back the jet manifold to accommodate the filter.
Some wand manifold will crush the filter during installation.