Projected separation of visual binaries as a function of primary mass for the Hyades (blue triangles and stars) and Pleiades (red diamonds) open clusters. The filled blue stars represent the very low-mass tight binaries discovered in this survey. The blue dashed lines marked the entire ranges of separation searched for companions in this survey, Reid & Gizis (1997) and Patience et al. (1998) in order of increasing primary mass while dotted lines indicate the completeness-defining minimum separation of the latter two surveys. The red dot-dashed lines indicate the equivalent limits for surveys in the Pleiades cluster (Bouvier et al. 1997; Bouy et al. 2006).