Important radii within the accretion disk; the distance between the accretor and the L1 point d_L1 (solid), the average equatorial Roche lobe radius (i.e. in the orbital plane) (dashed), the circularization radius R_circ (dash-dotted) and R_circ corrected for donor influence during free-fall, R_h (dotted, Eq. (19)). Furthermore, the pluses (+) indicate the outer tidally stable radius from Papaloizou & Pringle (1977). The stars ( ⋆ ) indicate the largest orbit that does not intersect others, according to Paczyński (1977) (which lies near the 3:1 resonance). The two open circles are outer disk estimates by Priedhorsky & Verbunt (1988), and the three filled triangles are outer disk radii from our SPH simulations.