A safety closure having a longitudinal axis, the safety closure comprising: an adaptor defining an axial bore and an outer radial surface, said outer radial surface defining a first plurality of radial ridges arranged in discrete groupings and a plurality of gaps extending in an axial direction between groupings of said first plurality of radial ridges, each of said first plurality of radial ridges extends generally perpendicular to said bore axis and comprises a first end and an opposing second end, and adjacent first radial ridges within a grouping of said first plurality of radial ridges are separated by a space; a cap including an inner radial surface defining a receiving space and a second plurality of radial ridges arranged in discrete groupings, said receiving space arranged to receive an upper portion of said adaptor and said second plurality of radial ridges arranged to selectively mate with and engage said first plurality of radial ridges of said adaptor to secure said cap on said adaptor, each of said second plurality of radial ridges extends generally perpendicular to said longitudinal axis and comprises a first end and an opposing second end, and adjacent second radial ridges of said plurality of radial ridges are separated by a space; at least one stopping structure located within said space between adjacent first radial ridges or within said space between adjacent second radial ridges, further wherein the stopping structure is adjacent said first ends of said adjacent first radial ridges or said adjacent second radial ridges, the at least one stopping structure being configured to limit relative rotation between said cap and said adaptor; and a locking system comprising a locking arm pivotally attached to an outer radial surface of said cap and including a lock piece arranged to selectively protrude into said receiving space of said cap to lock said first plurality of radial ridges in engagement with said second plurality of radial ridges, said lock piece being configured to engage said second end of at least one of said first plurality of radial ridges preventing the cap from moving from an engaged position to a disengaged position, said locking arm being pivotally attached to said outer radial surface of said cap such that said locking arm pivots about a pivot axis that is generally parallel to said longitudinal axis of said safety closure. an adaptor defining an axial bore and an outer radial surface, said outer radial surface defining a first plurality of radial ridges arranged in discrete groupings and a plurality of gaps extending in an axial direction between groupings of said first plurality of radial ridges, each of said first plurality of radial ridges extends generally perpendicular to said bore axis and comprises a first end and an opposing second end, and adjacent first radial ridges within a grouping of said first plurality of radial ridges are separated by a space; a cap including an inner radial surface defining a receiving space and a second plurality of radial ridges arranged in discrete groupings, said receiving space arranged to receive an upper portion of said adaptor and said second plurality of radial ridges arranged to selectively mate with and engage said first plurality of radial ridges of said adaptor to secure said cap on said adaptor, each of said second plurality of radial ridges extends generally perpendicular to said longitudinal axis and comprises a first end and an opposing second end, and adjacent second radial ridges of said plurality of radial ridges are separated by a space; at least one stopping structure located within said space between adjacent first radial ridges or within said space between adjacent second radial ridges, further wherein the stopping structure is adjacent said first ends of said adjacent first radial ridges or said adjacent second radial ridges, the at least one stopping structure being configured to limit relative rotation between said cap and said adaptor; and a locking system comprising a locking arm pivotally attached to an outer radial surface of said cap and including a lock piece arranged to selectively protrude into said receiving space of said cap to lock said first plurality of radial ridges in engagement with said second plurality of radial ridges, said lock piece being configured to engage said second end of at least one of said first plurality of radial ridges preventing the cap from moving from an engaged position to a disengaged position, said locking arm being pivotally attached to said outer radial surface of said cap such that said locking arm pivots about a pivot axis that is generally parallel to said longitudinal axis of said safety closure.