The classical T Tauri stars' spin rates are observed roughly an order of magnitude smaller than the breakup rates, which is not easily explained by hydrodynamic accretion. Magnetic coupling between accretion disks and protostars may be an explanation for the slow spin rates. We examine whether the general idea of magnetic braking depends on particular model parameters and initial conditions. We show that magnetic braking is a viable explanation for slow spin rates, which depends only very weakly on the model parameters and initial conditions. A large number of combinations of plausible initial conditions lead to final spin rates less than ～1/10 of the corresponding break-up rates within ～10~6 yr. The final slow spin rates converge to a narrow range which does not depend on initial spin rates. When the magnetic field is amplified during contraction and spin-up, the required initial field strength is roughly (2-3) x 10~2 G, which depends weakly on the exact nature of amplification. If the field remains constant throughout evolution, the field strength is required to be at least greater than 500 G for sufficient magnetic braking. The inner regions of accretion disks are truncated by the stellar magnetospheres. The truncation radius, R_0, is correlated with the final stellar spin rate, Ω_*, The final truncation radii lie at 3-10 stellar radii (R_*) with an approximate correlation, R_0/R_* ≈ 14[1 — 0.075(Ω_*/Ω_☉)], where Ω_☉ is the solar rotation rate. The spin-truncation radius correlation can be an interesting diagnostic tool for the magnetic braking model.
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