Finished riveting stabilator skins. The rivet grip call-out for the horn reinforcement appears to be wrong. The plans call for a CCPQ-42 but the stack up of Stabilator plate (0.032") + Actuator Horn (0.063") + Stabilator Channel (0.040") = 0.135" requires a CCPQ43 or 44 rivet. Performed a trial fit of the Trim Tab prior to riveting the Tab hinges, the tab rotates smoothly without binding and is centered . Next job will be to trim and install tips.