The stability properties of m > 2 tearing instabilities in tokamak plasmas are analyzed. A boundary layer theory is used to find asymptotic solutions to the ideal external kink equation which are used to obtain a simple analytic expression for the tearing instability parameter A'. This calculation generalizes previous work on this topic by considering more general toroidal equilibria q (however, toroidal coupling effects are ignored.) Constructions of A" are " obtained for plasmas with finite beta and for islands that have nonzero wiLdth. A simple heuristic estimate is given for the value of the saturated island width when the instability criterion is violated. A connection is made between the calculation of the asymptotic matching parameter in the finite beta and island width case to the nonlinear analog of the Glasser effect [A. H. Glasser, et al, Phys. Fluids 18, 875 (1975)].