According to the SolidWorks help files:
"Adds a second fillet to the existing symbol. This option is available for Square Butt, Single Bevel Butt, Single Bevel Butt with Root, and Single J Butt only. Type a size to the left of the symbol. Type a pitch to the right of the symbol."
I believe SW is following the ISO standard but I do not have that specification available to check.