First object

It selects the first of two objects required to define a fillet between two sides.

Select the second object

If lines, arcs or polylines are selected, their lengths adjust to accommodate the fillet arc.

If the selected objects are straight line segments of a polyline, they must be adjacent. More than  one fillet can exist between arcs. Select the objects near the location in which the endpoints of the fillet have to be.

Undo

Reverses the previous action in the command.

Polyline

It inserts two fillet arcs at each vertex of a polyline where two line segments meet.

Select the polyline:

Radius

It defines the radius of the fillet arc.

Specify fillet radius < current>: Specify a distance or press ENTER

The entered value becomes the current radius for the subsequent FILLET commands. Changing this value does not affect existing fillet arcs.

Trim

It controls if FILLET trims the selected edges to the fillet arc endpoints

Enter Trim mode option [Trim/No Trim] < current>: Enter an option or press ENTER

Trim

Trims the selected edges to the fillet arc endpoints.

No trim

Does not trim the selected edges.

Multiple

It rounds the edges of several sets of objects. FILLET repeatedly displays the main prompt and the Select second object prompt until ENTER is pressed to end the command.