The affix yat comes after ratha in the sense of 'this is his'.,
This debars अण् ॥ Thus रथस्येदं = रथ्यम् 'belonging to the chariot -- i.e. wheel or the axle.' The word रथ्य is confined to describe the parts of chariot. This rule applies also to compounds ending with रथ, as, परमरथ्यम्, उत्तमरथ्यम् because of the Vartika रथसीताहलेभ्यो यद्विधौ, after रथ, सीता and हल in applying the affix यत् there is tadanta-vidhi.,