Injection molded Black Salt Tank Lid fits most round brine tanks.
We can not guaranty a tight fit, but the lid should fit all 18" diameter round salt tanks including the Clack Locking tank ( just will not use the locking feature )The outer dimension is 18" and 9/16".
The inner dimension is 18" and 7/16".
NOTE: The BL18IM lid
can be used as a replacement lid for the Clack "locking lid" design,
but it will not have the "lock" feature, but otherwise it is a good fit as a replacement.
And since the Clack "locking lid" is not sold separately, this would be your best option should you be missing your lid.