The OPS INC™ 3 piece collar, often referred to as the Gordon Collar, was designed originally for use with the issued M4 rifles of the 90s. It allowed the M4 suppressor to be installed on a 14.5″ barrel with carbine gas system. The clearance cuts on the bottom allow it to be used with an FSB and clear the bayonet lug, however an FSB is not required for use. The 3 piece M4 collar has since become an iconic part of many clone rifles of the era.