The Harken 461 stand-up base allows a variety a blocks to be held upright and swivel and pivot freely.  Complementary hardware for the Harken 2670 Carbo Ratchet Mainsheet Block.  Found on PocketShip and any CLC sailboat with a mainsheet.

Specs:

• Height: 2"
• Weight: 4.5 ounces
• Base Diameter: 2 1/8"
• Inside Socket Diameter: 7/16"
• Pin Size: 1/4"
• Safe Working Load: 1000 lb
• Breaking Strength: 2500 lb
• Fastener Spacing: 1"