Culligan Housing Wrench 3-3/4 in. is expertly crafted to make cartridge s easier by loosening the bottom of housings with precision. This wrench is compatible with Culligan model US-550 and ACE model 4158515, ensuring a fit for your needs. To use, simply slide the circular end over the housing until it fits snugly, then unscrew carefully. It is important to note that this wrench is designed only for loosening; the bottom of the housing should be hand-tightened onto the cap to avoid cracking. This tool combines functionality and durability, making it an essential accessory for maintaining your water filtration system. Model Number: SW-1