Fastenings rhymes with:
happenings, openings, poisonings, questionings, seasonings, tightenings, bannings, beginnings, browning's, burnings, canings, corning's, drownings, earnings, earnings', evening's, evenings, fanning's, happenings, hennings, innings, jennings, leanings, lightnings, linings, manning's, meanings, mining's, morning's, mornings, openings, pennings, poisonings, questionings, runnings, screenings, seasonings, signings, tightenings, underpinnings, vining's, warnings, winings, winnings, yearnings
Fastenings sounds like:
factions, fastening, fasting, fastness, feasting, fictions, fighting, fighting's, fightings