A surgical anvil assembly for use with a circular stapling instrument, comprising: an anvil center rod; an anvil head having a post pivotally coupled to the anvil center rod, the anvil head being movable relative to the anvil center rod between a first, operative condition and a second, tilted condition; and a ring assembly disposed within a recess of the anvil head and movable within the recess from a proximal position preventing pivotal movement of the anvil head from the first, operative condition, to a distal position permitting pivotal movement of the anvil head to the second, tilted condition, wherein the ring assembly includes: a snap collar engaged to the post of the anvil head and configured to resist movement of the ring assembly out of the proximal position; a backup member supported on the snap collar and configured to engage the anvil center rod when the ring assembly is in the proximal position; and a cut ring captured between the snap collar and the backup member; wherein the post of the anvil head has an annular ledge disposed thereabout, the snap collar supported on the annular ledge and configured to flex outwardly to disengage the annular ledge upon receiving a distally-oriented threshold force to allow the ring assembly to move toward the distal position, wherein the snap collar includes an annular inner lip overlapping and supported on the annular ledge of the post of the anvil head when the ring assembly is in the proximal position, characterised in that the snap collar includes a plurality of horizontally-extending support surfaces and a plurality of vertical extensions having the annular inner lip extending radially inward therefrom, each vertical extension of the plurality of vertical extensions being disposed between a respective adjacent pair of support surfaces of the plurality of support surfaces; wherein the backup member includes: a ring body; and a pair of diametrically opposed tabs extending radially inward from the ring body, the pair of tabs being supported on a pair of diametrically opposed support surfaces of the plurality of support surfaces of the snap collar. an anvil center rod; an anvil head having a post pivotally coupled to the anvil center rod, the anvil head being movable relative to the anvil center rod between a first, operative condition and a second, tilted condition; and a ring assembly disposed within a recess of the anvil head and movable within the recess from a proximal position preventing pivotal movement of the anvil head from the first, operative condition, to a distal position permitting pivotal movement of the anvil head to the second, tilted condition, wherein the ring assembly includes: a snap collar engaged to the post of the anvil head and configured to resist movement of the ring assembly out of the proximal position; a backup member supported on the snap collar and configured to engage the anvil center rod when the ring assembly is in the proximal position; and a cut ring captured between the snap collar and the backup member; a snap collar engaged to the post of the anvil head and configured to resist movement of the ring assembly out of the proximal position; a backup member supported on the snap collar and configured to engage the anvil center rod when the ring assembly is in the proximal position; and a cut ring captured between the snap collar and the backup member; wherein the post of the anvil head has an annular ledge disposed thereabout, the snap collar supported on the annular ledge and configured to flex outwardly to disengage the annular ledge upon receiving a distally-oriented threshold force to allow the ring assembly to move toward the distal position, wherein the snap collar includes an annular inner lip overlapping and supported on the annular ledge of the post of the anvil head when the ring assembly is in the proximal position, characterised in that the snap collar includes a plurality of horizontally-extending support surfaces and a plurality of vertical extensions having the annular inner lip extending radially inward therefrom, each vertical extension of the plurality of vertical extensions being disposed between a respective adjacent pair of support surfaces of the plurality of support surfaces; wherein the backup member includes: a ring body; and a pair of diametrically opposed tabs extending radially inward from the ring body, the pair of tabs being supported on a pair of diametrically opposed support surfaces of the plurality of support surfaces of the snap collar.