If your ball head is a Bogen/Manfrotto model:
Most Bogen, Gitzo, and Manfrotto quick release clamps (QR) are not Arca-Swiss geometry and are not compatible with Wimberley Arca-Swiss style QR plates, thus cannot be used with the Sidekick. Most Manfrotto and Gitzo QR plate/clamp combinations include QR plates of a certain width, length and height that are contained within model-specific clamps with matching-geometry plate housings. This is to insure that you will use the manufacturer's plate with the manufacturer's clamp and vice-versa.
These set-width, specific-geometry clamps will not readily accept the Arca-Swiss style plate geometry, and even if it appears that some will fit, it is highly likely that the plate/clamp connection will not be secure or safe. Arca-Swiss style clamps (Wimberley, Kirk Enterprises, Really Right Stuff among others) are more universal and allow most any Arca-Swiss style plate to move forward and backward within the clamp, thus increasing the level of cross compatibility between manufacturers and increased versatility for the consumer.
To use these ball heads with Wimberley QR plates or the Sidekick, it may be possible for you to remove the existing QR clamp (or mounting platform) and install a Wimberley QR clamp permanently to the ball head stem. We sell the C-12 clamp which is packaged with the proper mounting hardware and designed to fit on the stem of a variety of ball heads.
See our C-12 compatibility page for a list of compatible ball heads and instructions on how to retrofit your specific ball head.