FIELD: medicine.SUBSTANCE: group of inventions refers to an improved adapter, for example, an adapter with a Luer nozzle, for use with a drug delivery device, and to a drug delivery device having such an improved adapter, to a method for adapter installation on such a drug delivery device and to an assembly, containing such an improved adapter and a connecting element connected to the said adapter. The adapter (10) is intended for installation on the distal tip (2) of the drug delivery device (1). The distal tip has an axial channel (3) to move the drug contained in the drug delivery device. The adapter has a longitudinal axis A aligned on the axial channel. The adapter comprises connecting means (34) to attach the adapter to the connecting element. The adapter further comprises an inner ring (20) configured to be removably engaged on the distal tip and compression means (30, 32) separate from the inner ring and intended for non-removable snapping on the inner ring meshed on the distal tip by proximal movement of the compression means relative to the inner ring. The compression means are adapted to apply a pressure directed towards the center to the inner ring so as to prevent axial movement of the inner ring relative to the distal tip. The inner ring comprises an annular wall (21) adapted to expand outwards radially under pressure applied radially outwards to the inner surface (21c) of the annular wall and configured to be compressed inward radially under pressure applied radially inside on the outer surface (21d) of the annular wall. The compression means comprise an outer ring (30) adapted to receive at least the inner ring at least partially. The outer ring comprises an inner radial rim (32) adapted to apply a pressure directed to the center of the outer surface (21d) of the annular wall (21) when the compression means are latched onto the inner ring. The annular wall (21) has a longitudinal slot (23) along a portion of its circumference. The longitudinal slot e
