Combination Oppenheimer with Knuckle Bender - to dorsiflex wrist and flex MCP joints, includes two attachments to extend/flex distal finger joints. Sizing: Measure distance across metacarpal heads on dorsal surface from radial aspect of second metacarpal head to ulnar aspect of fifth metacarpal head. Small: 2-1/2" Medium: 3" Large: 3-1/2"