An earplug (100) for a hearing aid includes an ear canal body part (103) with a bore (106) and a sound output passage (107) in communication with the bore and leading to a sound output opening (105) and flanges (104a-d) surrounding said ear canal body part and adapted to engage a wall of an ear canal. The flanges are substantially disc shaped and have an axis of symmetry that is substantially parallel to the axis of symmetry of the bore of the ear canal body part. The invention further provides a hearing aid and a method of inserting a probe tube in an earplug.