arc.padRadius()

arc.padRadius([radius])

If radius is specified, sets the pad radius to the specified function or number and returns this arc generator. If radius is not specified, returns the current pad radius accessor, which defaults to null, indicating that the pad radius should be automatically computed as sqrt(innerRadius * innerRadius + outerRadius * outerRadius). The pad radius determines the fixed linear distance separating adjacent arcs, defined as padRadius * padAngle.