An anti-splaying system comprising: a receiver having a base, a first arm, a second arm, a first locking channel, and a second locking channel, the first arm and the second arm each extending from the base defining a rod-receiving cavity between the arms, the first and second arms including first and second inner threads formed in respective inner surfaces of the first and second arms, and the first locking channel being formed in the inner surface of the first arm and extending along a majority of the first inner threads, and the second locking channel being formed in the inner surface of the second arm and extending along a majority of the second inner threads; and a set screw having a driving portion, a body portion, external threads extending from the body portion, and a distal locking component, the driving portion being connected to the body portion, and the distal locking component being connected rotatably to the body portion; wherein the distal locking component of the set screw and the locking channels of the receiver are configured such that the locking component can, in operation of the system, be moved into a securing position in the locking channels and, when in the secured position, fixes the two arms from splaying away from each other, wherein the distal locking component comprises opposing lateral ends sized and shaped corresponding to size and shape of the locking channels, for mating engagement between the locking component and the locking channels, wherein the lateral ends comprises opposing shoulders sized and shaped to engage opposing shoulders of respective ones of the locking channels, wherein the first and second locking channels extend distally beyond a bottom of the first and second inner threads, respectively, by an amount equal generally to at least a height of the locking component, when the system is assembled; characterized in that the distal locking component is plate shaped. a receiver having a base, a first arm, a second arm, a first locking channel, and a second locking channel, the first arm and the second arm each extending from the base defining a rod-receiving cavity between the arms, the first and second arms including first and second inner threads formed in respective inner surfaces of the first and second arms, and the first locking channel being formed in the inner surface of the first arm and extending along a majority of the first inner threads, and the second locking channel being formed in the inner surface of the second arm and extending along a majority of the second inner threads; and a set screw having a driving portion, a body portion, external threads extending from the body portion, and a distal locking component, the driving portion being connected to the body portion, and the distal locking component being connected rotatably to the body portion; wherein the distal locking component of the set screw and the locking channels of the receiver are configured such that the locking component can, in operation of the system, be moved into a securing position in the locking channels and, when in the secured position, fixes the two arms from splaying away from each other, wherein the distal locking component comprises opposing lateral ends sized and shaped corresponding to size and shape of the locking channels, for mating engagement between the locking component and the locking channels, wherein the lateral ends comprises opposing shoulders sized and shaped to engage opposing shoulders of respective ones of the locking channels, wherein the first and second locking channels extend distally beyond a bottom of the first and second inner threads, respectively, by an amount equal generally to at least a height of the locking component, when the system is assembled; characterized in that the distal locking component is plate shaped.