A tool (1) to insert a plurality of elongated flexible electric conductors (4) into the slots (3) of an elongated flexible insulating housing (2). The tool (1) has a passage (13) through which the housing (2) and conductors (4) move to have the conductors (4) urged into the slot (3). The passage (13) is bordered by a plurality of ramps (10) which engages the conductors (4) to urge them into the slot (3).