A lampholder has an outer sleeve centered on an axis and having a radially inwardly projecting lug having an axially inwardly directed end face and an inner core adapted to fit with a lamp, fittable inside the sleeve, and formed with an axially inwardly directed face axially alignable and engageable with the outer-sleeve end face on rotation of the core in the sleeve in a predetermined sense in a fully inserted position of the inner core in the sleeve. Interengageable retaining formations on the core and on the sleeve inhibit rotation of the core in the sleeve opposite to the predetermined sense when the faces are axially aligned with and engage each other.