I've often been disappointed with Obitsu 60 optional hands. Not only is the quality nowhere near as good as Dollfie Dream hands, the selection is also extremely limited. Trying to use DD hands on an Obitsu wrist frame will result in the hand falling off. DD wrist frames also don't fit onto Obitsu 60 arm parts. These problems will disappear today with some modifications.
This is the default Obitsu 60 wrist frame.
There's nothing special about it.
The basic idea here is to draw an outline of where to cut. I didn't measure anything with the image above and it's obviously not symmetrical. For your actual Obitsu 60 wrist frame, you might want to measure carefully instead of doing everything by sight like I did.
The vertical lines you cut will now allow you to use pliers to easily break off the excess pieces.
This is what your Obitsu 60 wrist frame should now look like.
We'll now take this piece from the Volks wrist frame...
...and transplant it to the modified Obitsu 60 wrist frame.
...slipping on the DD "Rock Fist" hand.
Your Obitsu 60 wrist frame is now 100% compatible with Dollfie Dream hands.
While you're permanently altering the Obitsu 60 wrist frame with this mod, You can still use Obitsu 60 hands if you want to go back to them for any reason.
About the only thing to be careful with after the modification is over would be how you remove the hands. If you try to slip them off by tugging at the hands at an angle, you may dislodge the Volks part from the Obitsu part in a way which will make the Volks part remain inside the hand. While you can easily retrieve the Volks piece if this happens, it's best to make sure that doesn't happen in the first place.