Originally Posted by patham
If you're referring to the groove at the front of the lens then that is for attaching the macro ring light. It's quite a bit wider than the hood-specific groove on lenses like the 85mm f/1.8.
There's a good chance you could fit a clip on hood on the groove but you'd need to find one with the right size and it'd probably be wobbly because the groove is larger than the groove used for hoods.
Paul.