Fillet
The Fillet 
tool is used to create a fillet on a
corner of a polyline by specifying its radius.
Creating a single fillet
Type in the fillet radius and click near a corner to create a fillet.
Creating fillets on all corners
You can apply fillet to all corners (as shown in the below image) by holding down the Ctrl key when clicking near a corner. This will create fillets on all corners of the polyline at once.
| The fillet is created only if both the segments meeting at the corner are straight line segments, and of sufficient length. |