Receptance coupling methods for predicting tool point dynamics often use an adapter or calibration gauge for extracting the spindle-tool interface dynamics. This, however, necessitates the measurement of the rotation to force and rotation to moment receptances at the free end of the clamped adapter which is difficult to measure practically. The present article provides a new method for determining the rotation to moment receptance as part of the Receptance Coupling Substructure Analysis (RCSA). The formulations in the current literature, suffer from several disadvantages such as having to use several calibration gauges, complex mathematical formulations, multiple measurements of direct and cross receptances, etc. The proposed approach overcomes these disadvantages by providing a simpler formulation with only three measured receptance on a single adapter. A modal parameter approach is used which shows better prediction of the rotation to moment receptance and satisfactory conformity of the predicted TCP compliance with the measured compliance.