1 3/4" Clamp (Tube Clamp). Two required. Used with 2 each #30053 1/4 x 1 1/4 Carriage Bolt and #42550 1/4-20 Keps Locking Nut. Also available in #900003 MPS Hardware as well as #900002 TGS Hardware. Also #900011 CP24 Clamp Assembly and #728209 MPQ Lower Clamp Assembly.