(4) 4" Blades attach to ankle or wrist Omni-directional resistance training Most effective for lower body, core and rehab training High intensity, low impact training for all fitness levels Most effective when used in conjunction with the upper body Bells. Can also be worn on wrist for added resistance or for those with hand limitations. This is our lowest resistance level fin, generally for those participating in aquatic therapy or needing to perform at very high speed for extended duration.