0.012 Inch - Medium Flow
It works with most 1/4" OD flexible tubing.
Depending on the Misting Pump size; Mid or High pressure. These would work for a softening system.
Mid Pressure: Calcium Inhibitor Filter - Poly Phosphate Filter: Link: https://mistcooling.com/misting-calcium-inhibitor-filter-poly-phosphate-filter.html
High Pressure: 5in Commercial Filter. Link: https://mistcooling.com/commercial-filter-for-mist-pumps.html
Any large than the filters mentioned would be recommended for Hard Water.
The cartridge inside the housing should be changed every 6 months
If you are on the website scowl down to Description or Specifications.
Filter housings are rated for up to 125psi.
5 microns. You don't need to worry much about the GPM as this is used before the pump. You just want to make sure that the filter is changed every six months so that the unit doesn't struggle to get water through to the pump.