The affix ṭhañ comes in the sense of 'occurring' and 'a commentary' after the name of a work to be explained provided that such work relates to a kratu or a yajña,
This debars अण् ॥ Kratu :- अग्निष्टोमिकः 'a commentary on a work on Aginshtoma sacrifices? वाजपेयिकः, राजसूयिकः ॥ yajna:- पाकयज्ञिकः, नावयज्ञिकः ॥
This sutra refers to words which are not antodatta. The words 'vajapeya' and 'rajasuya' are acute in the middle.
The words क्रतु and यज्ञ mean generally the same thing i.e. 'a sacrifice', but the separate mention of यज्ञ implies that the rule applies to yajnas other than Soma-yajnas because the word 'kratu' is technically applied to Soma-, sacrifices only. Thus पाञ्चौदनिकः, दाशौदनिकः ॥
The sutra is in the plural to prevent the application of the affix to the word-forms 'kratu' and 'yajna' 1.1.68.,