Threshold effects are a sensitive function of the mass of the isotopic substitute in the Li + FX (X = H, D, T) series of reactions. Quantum and quasiclassical calculations were carried out to find a rationale for these effects, Extended calculations were also performed to evaluate detailed reactive properties of the Li + FH reaction. This allowed an investigation of the applicability both of the J shifting model when evaluating the reactive cross sections from zero total angular momentum probabilities and of the main features of the reactive dynamics. Additional detailed tests of the suitability of the used PES were carried out by comparing calculated and measured detailed product properties.