Small Rudder Button Zinc 2-3/4"x 3/4"( RB-S ) Deep slotted stainless steel machine screw for maximum torque. Unit comes with both halves and screw/bolt making a full complete clam. Small mount with 1/4"-20X1-3/4" machine screw. Rudder Plates are designed in order to be streamlined, minimizing drag and turbulence.