Dictionary of Spoken Russian/Russian-English/Section 9

§9. VARIATIONS OF SOUND AND SPELLING IN NOUNS

Throughout the declension of nouns the habits of §3 and §4 will apply; we do not mention them specially for each noun.

сад [sat], but gs сада [sada]
кубок [kub'k], but gs кубка [kupka]
сад, np сады, but ключ, np ключи [-kji]; is with ending [-om]: столом, отцом, стулом, but рулём, музеем, автомобилем, перцем

Note especially the insertion of vowels when there is no ending.

трубка [-pk-], gp трубок [-b'k] ложка [-šk-], gp ложек [-ž'k]
кухня, gp кухонь
овца, gp овец
сестра, gp сестёр

but, for instance, звезда, gp звёзд; битва, gp витв, because [d] and [v] are not among the consonants before which a vowel is inserted.