Average collisional velocities in the low inclination γ_F = 25° case between equally sized (left panel) and differently sized planetesimals (right panel) for planetesimals centred around 10 AU from the central star. Left panel: collisions between 10 km–10 km bodies (green-solid); 1 km–1 km (blue-solid); 100 m–100 m (red-solid). Right panel: collisions between 10 km–1 km bodies (green-solid); 10 km–100 m (blue-solid); 1 km–100 m (red-solid). Threshold velocities for catastrophic disruption corresponding to the different size-combinations for the weak (dash-dotted line) and strong aggregates (dashed line) are also shown.