The Troy Hex Dumbbells' rubber resists cracking and fading while protecting floors and equipment. These dumbbells are made from solid cast iron with a 6-sided anti-roll hex design and encased in virgin rubber. This dumbbell set is stylish and durable. The dumbbell heads are securely attached with a unique pin mechanism which means this dumbell set is about as low-maintenance as it gets. No spinning or loosening.