This is the third Vibroplex model.  It has single contacts for both dots and dashes and was made in two versions.  The "Early" X, which is most common, has a square lever rod and a "T" shaped damper assembly.  The "Improved" X is more scarce because it was made for only two years beginning in 1919.  It has a round pendulum and round weights and a simple adjustable thumb screw damper assembly with no moving damper wheel.