In this paper, we explore the appealing possibility that the strong suppression of large-size QCD instantons – as evident from lattice data – is due to a surviving conformal space-time inversion symmetry. This symmetry is both suggested from the striking invariance of highquality lattice data for the instanton size distribution under inversion of the instanton size ρ → 〈ρ〉2/ρ and from the known...