SIZING: To choose your size, carefully measure the circumference around your thumb knuckle at the widest point, in inches. Size MEDIUM RIGHT fits your right hand and thumb knuckle circumferences between 2 5/8"-3". IF BETWEEN SIZES, ORDER THE SMALLER SIZE. Brace prevents thumb flexion and extension, helping alleviate pain associated with post-op recovery, arthritic thumbs, De Quervain’s tenosynovitis, gamekeeper's thumb, skier’s thumb, osteoarthritis, trigger thumb, ulnar collateral ligament (UCL) injuries, fractures, dislocations, sprains, etc. Saddle joint immobilizer can be worn beneath gloves and throughout the day for support while typing or during low-impact exercises and activities, for example. Rigid thumb splint is made out of a latex-free, perforated polyamide plastic and an elastic / medical-grade Velcro wrist strap, making it both durable and waterproof. To eliminate any discomfort throughout the day, a soft universally sized polyester undersleeve and extra padding is included to prevent the MCP thumb splint from rubbing or chafing against your skin.