The 2nd Generation joint blocks in Simscape Multibody define the primitive along one direction. For example, the Revolute Joint block represents a joint with one rotational degree of freedom along the common Z axis, as mentioned in the documentation:
You cannot change the primitive direction of rotation, but you can connect a Rigid Transform to the joint block. This change was made to add more flexibility in defining reference frames between solids and joints. Refer to the following documentation:
Here is an example that uses this technique rather than using First Generation blocks:
