They feature a raised chassis or section of chassis, enabling them to advance in parallel with the crop with left and right wheels on either side of one or more rows of the crop.
Bíonn fonnadh ardaithe nó cuid den fhonnadh ardaithe iontu, rud a fhágann gur féidir leo dul ar aghaidh i gcomhthreo leis an mbarr agus na rothaí ar gach aon taobh den líne bairr nó de na línte bairr.