Rectangle StrokeThickness
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="Microsoft.Samples.Graphics.RectangleExample" WindowTitle="Rectangle Example"> <Canvas> <Rectangle Width="100" Height="50" RadiusX="20" RadiusY="20" Stroke="Black" StrokeThickness="4" Canvas.Left="135" Canvas.Top="100" /> </Canvas> </Page>