The symmetry between W2 and CO (K spin symmetry) is one of important approximate global symmetries in our model. Some consequences of this symmetry are discussed, including the natural existence of cold dark matter with .l2cDM= 0(1) and the existence of very massive and quasi-stable hadrons. Implications of K symmetry for CP violations are also discussed. [1] At present, there exist two types of models beyond the standard model (SM). One is based on elementary lepton and quark and the other based on composite lepton and quark. Th~ typical example of the former is supersymmetric GUT models and of the latter is preon models. I) Both have some unique virtues, though lepton and quark, we think, have too complicated properties to construct a simple and beautiful theory of Nature by regarding them as fundamental matter. These models predict many new particles. Hence one of important criterions to the validity of models is how naturally predicted new particles settle the problems which cannot be understood in SM and how naturally they do not affect phenomena which can be understood well in SM, namely, naturalness in confrontation of the model with the real world. In order to clarify the viability of models, it is desirable to study phenomena based on the general structure of the model without relying on a delicate part of the model. In this paper we discuss implications of the symmetry between preons W2 and Co which is expected to hold approximately in our model. 2 )-5) [2] In our model there exist colorless preons WI, W2, Co, h and a colored preon Ci. The first three carry charges e/2, -e/2 and -e/2, respectively. All preons carry a preonic charge which is identified with a magnetic charge and a color magnetic charge. 2 ) Due to this unique feature, bound state of preons (BSP) is governed by dynamics which we do not know a detail of,namely, super-strong interaction even at a short distance and charge-pole system. Hence we cannot make a definite statement about a dynamical property of BSP at the present stage, though some plausible conjectures can be made such as a string behavior of BSP at a large distance due to a formation of magnetic flux tube and emergence of confinement of preons and of effective gauge theory at a low energy through its zero Regge slope limit. 3 ) In such a circumstance, it is adequate to discuss properties of BSP on the basis of the general property of the model. In our model the dominant interaction among preons is that due to a preonic charge, which is shared equally with preons wand c. Hence, SU(6)wc holds where preons wand C belong to .§. under SU(6)wc. 3