C?ng l m?t ki?u qu?ng co khc nh?ng h?p ?n qu?ng co th??ng s? c kch th??c nh? h?n b?ng qu?ng co. N th??ng ???c ?i km cng b?ng hi?u qu?ng co ho?c d?ng ??n l?. V? tr g?n h?p ?n th??ng l 2 bn hng ho?c ??t d??i ??t, ho?c b?t k? v? tr no d?a vo cng n?ng s? d?ng.