Sprocket-nose bar
A guide bar with a small toothed roller wheel set in its tip, so the chain rolls around the nose instead of sliding over it. The alternative is a hard-nose bar, in which the chain slides across a solid, usually stellite-faced tip.
Sprocket noses reduce friction at the point where the chain changes direction, which means less heat, less power lost and less wear — they are the standard fitment on almost all modern saws. The trade-off is a bearing that needs grease through a small port on some bars and that can fail if it is starved of oil or packed with grit; a nose sprocket that has seized or lost teeth must be replaced, not persevered with. Hard-nose bars survive abrasive work such as dirty or frozen timber better and have nothing to wear out, which is why they persist in specialist use.