The present invention is directed to a pen -type drug injection device having housing (1) comprising an outer shell (2) with an aperture, a transparent window-insert (4) received within the aperture and a clamp (3) attached to the outer shell (2). The window insert (4) has at least one recess (11) which is engaged by a lug (13) of the clamp (3) to retain the window-insert (4) within the aperture of the outer shell (2).
