RadDiagram does not render stroke thinner than 2px.
Code to reproduce:
<telerik:RadDiagram ID="webDiagram" runat="server">
<ShapesCollection>
<telerik:DiagramShape Id="s1">
<StrokeSettings Width="1" Color="grey" />
</telerik:DiagramShape>
</ShapesCollection>
</telerik:RadDiagram>
Actual result:
Expected result: