After the episode Bismuth, Amethyst got her whip upgraded. It has spiked balls at the end of how ever many tails it's got. Here's where Google comes in. There are weapons that fit the exact picture of her new weapon, a flail, and a mace. Just a quick heads up.
Whips - A strip of leather or flexible material used for PUNISH.
Mace - A handle, usually long, with a spiked ball at the end. Can have a chain/rope in between the handle and ball.
Flail - A handle, usually short, with a spike ball/s at the end separated by a long chain/s.
One more heads up, if your excuse is that Amethyst's weapon has a whip and not chain, Sugilite's weapon uses a whip and what's it? A flail.