Recently made experiments allowed measurement of effective data (free of crack tip shielding) and enabled a better understanding of intrinsic behaviour of shear-mode cracks. Influence of crystal structure and microstructure was distinguished. Experimental results for niobium showed that growth micromechanisms and effective thresholds (ΔKIIeff,th≈1.0MPam1/2, ΔKIIIeff,th≈1.4MPam1/2) of modes II and III cracks were different, which was also observed in other metals. Validity of the simple formula for mode II effective threshold for single-phase metals based on the dislocation emission model was confirmed. The cracks propagated in a coplanar manner along the maximum shear plane, which is a characteristic behaviour for bcc metals. Model of propagation of remote mode III loaded cracks by local mode II advances was confirmed.