Helm Products Fhc-series Permanent Rail Clamps . Similar to the HR-Series clamps but meant for more permanent installations. Bottom half of the clamp has 38 hex cavities to hold 10 nuts. Top half of clamp has clearance holes for bolts. U-grooves and stainless cover plates on the top trap 4 to 14 dia. wire. Stainless hardware included. Sold in pairs.