Part Number: FFA100. FIRM FLEX DUAL DRIVE UJ ADAPTER SET. Includes: 1/4” Spring Loaded Universal Joint adapter– Dual drive 1/4’’ Sq x 11mm Hex3/8” Spring Loaded Universal Joint adapter – Dual drive 3/8’’ Sq x 17mm Hex1/2” Spring Loaded Universal Joint adapter – Dual drive 1/2’’ Sq x 21mm Hex.