1: Hand joint that slips into the arm of an Excellent body
2: Extra Excellent hand joint
3: Extra Excellent hand joint with tip clipped
4: Extra Neo hand joint

a: Example of fixed hand joint
b: Proper alignment of joint in the hand.
c: Unaltered hand
d: Neo hand with Excellent style joint

I highly recommend using the Excellent hand joint for both Excellent and Neo hands. The post on the Neo hand joint (4) is very thin and flat sided. It will snap easily, leaving the post inside the hand, ruining the hand.

To add the long post (2), you will need to drill deeper into the hand with a dremel tool to make room for the smaller part of the post. If you do so, be very careful not to drill through the entire hand. Afterwards, push the post as far as it will go. The ball should be cupped by the end of the hand. Using this method, the post will be secure and needs no glue reinforcement. This is my preferred method because sometimes when posing the hand, it does help to be able to spin the hand around on this small post.

To add the small post (3), clip the tip of the joint and push it inside the hand. I recommend super glue or zap-a-gap to secure the post. Make sure you don't get any glue residue on the hand and make sure that the joint is correctly upright (b) in the hand. Which side it is upright on does not matter. In the photo above (b) it is on the right side.

To add an Excellent post to a NEO extra hand, soften the hand by running it under hot water, briefly boiling it, or heating with a blow dryer, the push a short post(3) inside. When the hand cools, the vinyl with shrink around the post and secure it inside without needing glue. It might take a bit of strength to push the post inside, but it will work.