Change the stroke properties of an object
In the Tools panel in Microsoft Expression Blend, click Selection, and then select the object for which you want to adjust the stroke properties.
Under Brushes in the Properties panel, make sure that Stroke is selected.
Under Appearance in the Properties panel, do one or more of the following:
To set the stroke width, select a value for the desired stroke width next to StrokeThickness. The value of the stroke width is measured in pixels (or, device-independent units which are approximately 1/96 inch). Change the value to 0 if you don't want the object to have any stroke width applied to it.
To set the corner join, click one of the following next to StrokeLineJoin:
Miter For a pointed corner.
Bevel For a squared-off corner.
Round For a rounded corner.
To set the miter limit, use the value slider, or type in a value next StrokeMiterLimit. The miter limit can only be set when Miter is selected as the corner join. The miter limit describes how long the point of a miter join can get before it is automatically squared off into a bevel join.
To set the end cap style, click one of the following next to StrokeStartLineCap or StrokeEndLineCap (or both):
Flat To create a squared-off end cap.
Square To create an end cap that extends beyond the end point by one half the width of the stroke.
Round To create a rounded end cap.
Triangle To create a pointed end cap.