Primary V -band magnitude against magnitude difference between primary and secondary for binaries produced by gravitational-collapse simulations. Particle masses were converted into a spherical radius (assuming uniform density), which was then converted into a magnitude using a fixed albedo and distance. As with Fig. 2, marker colour and shape indicate the initial cloud mass, and any N > 2 systems are represented by smaller, fainter markers. The mass ratio for a given magnitude difference is shown on the upper x-axis. The vertical line indicates the mass ratio cut-off of m₂∕m₁ ≥ 10⁻³ in the orbit-search algorithm. The observed TNBs from Grundy (2019) are shown as black crosses. We represent “special cases” and dwarf planets as red plusses. The red circle with error bars represents how Arrokoth (2014 MU₆₉) would appear if its components could be separately resolved. An approximate empirical detection limit (Noll et al. 2008) and a lower magnitude limit of 25 are shown as dotted red lines.