Smart　materials　responsive　to　stimuli　and　new　rotary　mechanisms　have　drawn　much　attention　in　recent　years.　This　paper　investigates　a　novel　snap-through　rotation　mechanism　of　a　thermal　responsive　bimetal　ring　confined　inside　the　annular　region　constraint　when　subjected　to　the　local　curvature　induced　by　thermal　loading.　The　buckled　ring　has　movable　boundaries　and　keeps　an　invariant　shape　during　the　snap-through　rotation　so　that　it　requires　small　energy　input　to　drive　the　bistable　transition.　To　uncover　the　elusive　mechanism　behind　this　intriguing　snap-through　phenomenon,　a　theory　based　on　the　bifurcation　and　energy　principle　is　developed　to　predict　the　critical　loading　curvature　and　the　critical　loading　temperature,　which　agrees　with　the　experimental　results.　The　effects　of　loading　positions　and　the　constraint　width　are　studied　and　a　map　predicting　the　critical　loading　curvature　with　different　geometrical　parameters　is　demonstrated.　The　rotary　buckled　ring　not　only　enables　the　bistable　actuation,　but　also　triggers　various　actuation　applications　such　as　the　motor　actuation　and　the　pump　actuation.　Due　to　great　advantages　in　terms　of　energy　supply　and　actuation　loading,　this　study　exhibits　great　potential　of　the　proposed　snap-through　mechanism　in　bistable　structures　and　rotary　actuation.　©　2024　Elsevier　B.V.