Single extension drawer slides are 17 mm high and will successfully replace worn out runners in units from MFI, IKEA, Argos and any other where 17 mm slide runners were used. This type of runner fits within a groove half way down the side of your drawer. The high of the groove is 17 mm. To find the size you need close your runner and measure this length. This does not have to be an exact match just as long as the runner is shorter than the depth of your cabinet. The longer the runner, the better the opening of the drawer. The extended length is just given as information and is not a critical dimension. This is the length of the runner when fully opened.