'B' Tube clamp (Tube Clamp). 2 required. One part of assembly that secures center section to bottom. Also requires 2 each; #20413 1 3/4 Tube Clamp, #20417 Link and 4 each;30052 1/4-20 x 3/4 Carriage Bolt and #42550 1/4-20 Keps Locking Nut. Also available in #900011 CP24 Clamp Assembly.