The affix aṇ comes after a word in the Instrumental -3rd case in construction in the sense of 'surrounded' the thing so surrounded being 'a chariot'.,
Thus वस्त्रेण परिवृतो रथः = वास्त्रः \a chariot surrounded with cloth\. So also काम्बलः, चार्मणः ॥ Why do we say 'the thing so surrounded being a chariot?' Observe वस्त्रेण परिवृतः कायः 'the body surrounded with cloth' the word परिवृत means covered from all sides. The affix will not be used if the chariot is not completely surrounded. As छात्रैः परिवृतो रथः ॥,