A shock attenuator capable for use with a high pressure fluid line at pressures experienced by waterjet cutting systems comprises an attenuator body having an internal generally axially-extending bore extending between end regions, at least one of which is open-ended. An end plug within the open-ended region of the bore seals the bore and has a though hole for accommodating a fitting for connection to a high pressure fluid line. A closure assembly for retaining the end plug within the bore includes a first plurality of generally radially-extending tabs extending from the attenuator body and circumferentially disposed about said axis, with each of said tabs of the first plurality being separated from the next tab by a respective gap. A second plurality of generally radially-extending tabs is coupled to the end plug and circumferentially disposed about said axis, with each of said tabs also being separated from the next tab by a respective gap. The second plurality of tabs is positioned for retention by said first plurality of tabs in such a way that the end plug is retained in the bore when subjected to the high pressure from high pressure fluid within the bore.In one embodiment, the first plurality of tabs extends outward from the body's exterior to engage the second plurality of tabs extending inwardly from an end cap.In another embodiment, the first plurality of tabs extends inwardly from the bore's wall to engage a second plurality of tabs extending outwardly from the end plug.