The 3M Model A2 Replacement Cartridge is designed for use in the 3M Recreational Vehicle/Marine Filtration Systems WV-B2, US-A1, and US-B1. NSF Tested and Certified. Part number 5613323
A2 Specifications:
The Model A-2 should be changed every 1 year or 7500 Gallons depending on water quality and usage.