Original OEM coreless Bullfrog Spa Replacement filter for A series, R series, and X series for late 2017 models with standpipe. This Bullfrog replacement filter is specially designed for 2017 and newer Bullfrog Spas that have the plastic standpipe and cap in the filter housing. This filter does not have threads on the bottom! For Bullfrog Spas year models ranging from 2013-2017 requiring threaded bottom, please purchase Bullfrog Spas replacement filter (10-2870). Please feel free to call us at (972) 317-1011 if you have any questions about the replacement filters on your Bullfrog Spa!