Ball end chain link modifications

Modify the existing file in order that when they are linked they freely move as a linked chain. There are really just 2 dimensions that need modification. The 2 changes are the centersection need to be round and the length of the link needs to be longer to permit the links to freely swing. To insure this actually works you may need to do a 3 d animation. I am sending STL and a SLDPRT files. I need to get this 3d printed when complete.