Stand-up bases allow a wide variety of blocks to be held upright, swivel freely, and pivot for fairleads under load. Ball and Socket Swivel Bases The ball and socket design allows blocks to swivel freely and pivot to a 45 degree angle. Bases may be fitted with springs but block won�t hit the deck without them. Select blocks carefully as the maximum working load of either base is often less than corresponding blocks. Stanchion Mount Base The 061 stanchion mount base attaches blocks to 7/8 in or 1 in (22 or 25 mm) stanchions or pulpits and is often used to lead furling lines to the cockpit. Allows blocks to swivel and pivot for fairleads. Midrange Stand-Up Use the 1573 stand-up base with Midrange blocks. The low-profile design is ideal as a mastbase halyard lead block. Combine the 1573 with single Midrange ratchet or Fiddle blocks. Doubles and triples will fit the 1573, but their safe working loads are higher than the base. Springs Springs are used to support blocks on padeyes, eyestraps, bases and traveler cars. Keeps blocks from hitting the deck. Stand-up Boots Made of durable flexible PVC, stand-up boots hold blocks up without snagging lines. The 369 fits 40 mm and 57 mm Carbo and Black Magic� blocks. The 370 fits 75 mm Carbo blocks.