Self-guiding cutters for rounding over edges do not require a side fence.
They are supplied with two bearings.
Use the larger bearing for a round-over.
If the cutter is lowered a top quirk can be produced.
A full round/bullnose for stair treads can also be produced by taking a second pass from the opposite side of the workpiece.

Specification:
D=18.7 mm
C=3/8 inch
C=9.5 mm
B=9.5 mm
B2=12.7 mm
R=3 mm
OL=58 mm
Shank Diameter=1/2 inch