Split shot sinkers have a a groove that runs along the length of the sinker. Its purpose is to attach the sinker to the fishing line. Rubber core sinkers use ribber in the middle of the sinker to attach the sinker to the line. Advantage of using rubber sinkers is that they can be attached quickly and these sinkers do not damage the fishing line. Bell sinkers are round shaped and therefore are prefered for trolling and off shore anglers. Their bell roundness allows for smoother interactions with objects in water and prevents tangle up.