Hi, we checked the sigma art 24-35mm f2 lens size is 82mm, please reconfirm it , if the lens size is 82mm, this square filter holder system kit can fit it ,thanks. 

Yes. A very small one, but it's there! 

Hi, this is filter adapter rings, support use larger or small size filter on your lens , not related with camera brand. 

67mm should also be stenciled on the front edge of the lens somewhere. If so, then you should be good to go. It should be on the lens because a lens cap can be lost or broken. 

The adapter clicks on the lens. It has a small dark gray colored lever (not the white plastic tab to change aperture), level to the outer edge of the bottom ring accessible when removed from the camera, grab the whole adapter with your left hand and push the lever in with your thumb, and while pushing, rotate the lens with your right hand to remove it. You need to push in that lever to unlock the lens.