These are the same indicators you have seen Phil and others use on television shows such as The New Fly Fisher. Don't accept the imitators, get the real deal.
The black peg pinches a loop of leader/tippet against the indicator, holding it in place; and once a strike is recognized the loop is released, allowing the indicator to slide free. It does not interfere with landing the fish in any way.
Simply superior for fly-fishing stillwaters, and even rivers and streams. Perfect for indicator fishing.
Tapered or round, 4 per package.