Abstract: A plastics zip for clothing has two mutually engagable male (203) and female (204) zip profiles of generally uniform cross section along the whole or part of their length and merged or demerged within a special slider (115). The slider has two guide slots (116, 117) which join to create a Y-shaped passageway within the body of the slider and side slits (118, 119) to allow the slider to move along the fixed tapes or flanges (108, 109) of the zip profiles. One of the guide slots contains an expansion element (226) which opens the jaws of the female profile allowing it pass over and capture the smaller male profile so that the zip is merged. Movement of the slider in the opposite direction allows the two profiles to be demerged and exit from the slider.