Jig heads are the top parts of lures known as jigs, used to catch a wide variety of predatory fish species. Jig heads may come by themselves, or as a complete package, usually with a skirt trailing the head and covering the hook. Usually, the hook extends down from the jig head as one piece. Therefore, jig heads are not just the top of the bait, but the hooking mechanism as well.
The sizes of jig heads often depend on the fish species being sought. In some cases, a smaller head may be good for species like crappie, which do not grow very big. In other cases, a larger jig head may be desired to catch species such as walleye and largemouth bass. In general, jig heads come in weights less than 2 ounces (56 grams) for fresh water fishing.
The use of jig heads in salt water can have slightly more variation to the sizes. However, in the vast majority still stay relatively small. Some deep sea jigging techniques may require jig heads to be slightly larger than the freshwater versions, however. Again, this usually depends on the type of species being targeted.
While many jig heads come as complete jigs, there are those which do not. The main reason for jig heads to be sold separately is to allow the angler to choose the skirt they think will be most effective. The angler may want to choose a different color or length. This allows the opportunity to do that.
Often, fishing is a process where baits may need to be tried in more than one combination or more than one area. Having jig heads with interchangeable skirts offers a whole new element to the process. This may be especially critical for those anglers fishing in tournaments, who need to find the right lures and find them quickly.
Most jig heads are made with a lead head, which gives them the weight they need. Further, this allows the angler not to have to use an additional weight, which may interfere with the presentation of the jig. That is why the jig head doubles as a weight.
In general, a weight of 2 ounces (56 grams) or more is not needed in fresh water. However, in salt water, if trolling at a high rate of speed for larger species, a heavier weight may be required. This accounts for the difference in the weights of jig heads between fresh water and salt water.