U-drop crystal chandelier prisms are frequently found hanging from a chandelier's bobeche or top bowl. They refract light well and are inexpensive so they can be used when you need a lot of an item to fill out a chandelier. They are identified by the long narrow shape that looks like the tip of a narrow arrow. They do come in various sizes up to 6 inces or so and they come in a rainbow of colors.
ChandelierParts.com offers about 25 colors in many sizes. They are usually used with a top bead which might be the same color, different complimentary color or clear. They can also have a notch to add style and refract a bit more light.
The point cut crystal prism is identified by the cuts and facets on the body of the prism and the narrowing of the prism to a sharp tip. The characteristic that separates it from the U-drop is that it is shorter than it's more slender cousin.
Point cut prisms come in clear as well as a wide variety of other colors, styles and sizes. Point cut prisms are popluar around abobeche, hanging from chains, or anywhere on a chandelier when you need many prisms to catch and refract light. They are a very common chandelier part used world wide.