If you deal with both metric and US units based diagrams then it can be useful to understand how Visio goes about surfacing the correct stencil under the 'More Shapes' menu. This, of course goes double if you're creating stencils yourself, so I thought I describe how things work below.
Content Discovery
Before I look at the process let's go over the three main ways that Visio uses to discover what content (stencils, templates and addons) it has access to. Broadly these are:
- My Shapes
- Path Discovery
- Publishing
'My Shapes' is a specially named folder, usually under the user's Documents directory.
Path Discovery is the original method that Visio has used and allows you to set an number of file locations* through which Visio will search. (*see File / Options / Advanced / File Locations)
Publishing is a more recent addition that allows developers to build certain attributes about the content, which are then 'published' to the registry. This brings a number of benefits such as being able to separate the physical path of the file from the UI visible location and additional things like language specific file versions. This is used together with a special registry key that, when changed, flags to Visio that it needs to re-survey the registry.
I included a bit more detail about content discovery in this video [00:38:20] that you may want to watch that if you're interested.
With that background out of the way let's move on to look at what happens in the 'More Shapes' menu.
'More Shapes'
The choice of which stencils appear under the 'More Shapes' is governed by a combination of the units of active page (DrawingScale cell) and the stencil file name.
Broadly, any file under 'My Shapes' (note 'My' not 'More') will be displayed irrespective of the active page units. For all other stencils based on Path Discovery and Publishing Visio looks at the stencil file name - if it ends with an "_M" then it will only be displayed with page of the metric units and, if it ends with "_U" or has no underscore ending, it will only be displayed if the active page units are US based.
[Note that there's nothing to prevent you opening a metric stencil with a US units drawing. The workspace information will still allow you to save the metric stencil and drawing together. This process just describes the way in the 'More Shapes' menu decides what to display.]
In order to try and explain this a little more clearly I've put together a chart describing the choices (click on the image for a 100% view):
