- Replacement micro-adjust single-hand helmet retention system - Includes reflective sticker - Simple to install without special tools or training - Compatible with O`Neal Defender Helmet, all sizes black One Size MTB 26% Polypropylene, 26% ABS, 22% Nylon, 9% Polyester, 9% TPE, 4% Polyformaldehyde, 4% Metal DEFENDER Helmet