Currently there is no block that directly interface between the 3D and 1D domains. However, it is possible to do this by porting force and velocity information across the domains as physical signals. A "Force Sensor" block in the 1D domain can send a signal that applies the force to a joint in the 3D domain. Then the velocity of the 3D component can be constrained to the velocity of the 1D component by passing a measured velocity physical signal to a "Velocity Source" block in the 1D domain. To see how this is done take a look at the following examples:
Also, the "Simscape Multibody Multiphysics Library" on MathWorks File Exchange contains several interface blocks for interfacing between the 3D Multibody domain and the 1D translational and rotational Simscape domains. It also includes blocks for modeling hydromechanical and electromechanical systems. Note that "Simscape Multibody Multiphysics Library" is not an officially supported MathWorks product.