Helm FHC-12 7/8" & 1" RAil Clamps This multi-purpose clamp is for more permanent installations. Ideal for use with fishing gear, instruments, sonar, etc. Designed for mounting most of Helm's rail mounted holders for fenders, ring buoys, etc. Bottom half of clamp has 3/8" hex cavities to hold #10 nuts in place. Top half of clamp has clearance holes for bolts. The "U" grooves in the top half are for trapping #4 to 1/4" diameter wire. Stainless steel cover plates are supplied for this purpose, and can be used as a template to drill holes in unit to be mounted. With the reducing inserts, one model fits two rail sizes. A 1 1/4" square rail model si also available. The clamps are durable black nylon. Stainless steel mounting hardware is supplied. Two