Detonator assembly placement

A device for positioning a detonator assembly in a borehole wherein the detonator assembly includes an elongate body with a first end and an opposed second end, the device comprising a housing, a volume inside the housing with a central axis, a mouth on the housing through which the first end of the body is insertable into the volume, at least one formation on the housing configured to engage with the first end of the body thereby to retain the first end inside the volume and leave a portion of the body including the second end outside the volume, wherein the housing includes a wall with a plurality of apertures which are evenly spaced from one another in a circumferential sense extending around the central axis and wherein at a lower end of each aperture the wall includes a number of recessed formations and a plurality of retention members, each of which includes a respective base which is engageable with a respective one of the recessed formations on the housing, and at least one elongate flexible element which extends from each respective base radially outwardly relative to each base and at an acute angle relative to the central axis.