You may not want to use the standard Visio UML stencils to draw UML diagrams. Earlier versions of Visio used The UML v1 constructs, so some may be out of date.
An excellent set of UML stencils are available. Credit to their maintainer - Pavel Hruby.
Pavel’s Visio stencils cover version 2.5 of the UML specification and support multiple versions of Visio.
Additionally, Pavel maintains SysML stencils too. SysML is a general purpose modelling language for complex systems that may include hardware, software, information, personnel, procedures, and facilities. SysML is beyond the scope of these pages. Further information can be found here.