  We investigate helicity amplitudes (HAs) of $A \to B C$-type decays for
arbitrary spin towards the kinematic endpoint. We show that they are
proportional to product of Clebsch-Gordan coefficients (CGC) and the velocity
to some positive power. The latter can be zero in which case the HA is
non-vanishing at the endpoint. In essence the spatial rotational symmetry,
broken by the relative spatial momenta of the particles, is restored at the
kinematic endpoint. Therefore SO(3) and SU(2), for bosons and fermion in the
decay, act like a global internal symmetry groups. Some of our results can be
understood in terms of the Wigner- Eckart theorem. The findings are useful for
i) checking theoretical computations and ii) the case where there is a sequence
of decays, say $B \to B_1B_2$ with the pair $(B_1B_2)$ not interacting
(significantly) with the $C$-particle. An example is $H \to Z Z^* \to 4\ell$
where our findings might be of use for experimentally determining the Higgs
quantum numbers. Angular observables, which are essentially ratios of HAs, are
given by ratios of CGC at the endpoint. We briefly discuss power corrections in
the velocity to the leading order.
