These thumb grip and hand grip are designed based on the contour of the original camera and therefore they are prefectly fit if you have a grip of any brand. However, If you do not use a grip getting just a thumb grip is not advised because without a grip you hand will natually move closer to the center and your thumb will be closer to the center of the camera. 

Therefore we have changed the package by removing the option of just buying the thumb grip. We have now two option. 

Just hand grip package (Hand grip + C-Loop)

Full package (Hand grip + Thumb grip + C-Loop)