IST Fin Strap Compatibility: Specifically designed for use with IST FK-30, FK-31, and FK-09 watersports fins, and pairs perfectly with FBK-31 fin buckles for easy adjustment and comfort. Adjustable Rubber Heel Strap: Provides a secure, personalized fit, ensuring your fins stay in place throughout the dive. Durable and Reliable: Built to withstand frequent use in harsh saltwater conditions, offering long-lasting comfort and performance for divers of all levels. Two Design Available: This item may come in one of two compatible designs as shown in the photos The IST Scuba Diving Fin Strap is designed for maximum comfort and ease of use. Its adjustable neoprene heel strap ensures a snug fit while its quick-release buckle allows for easy on-and-off. This durable strap is a must-have for your dive gear.