Blind hole mounting kits are used when inside access to the mounting points is not available. The mounting screws are inserted through holes, drilled through the ladder racks vertical rails, and are threaded into inserts placed in the truck body panel. The holes in the ladder rack vertical rails can be drilled by the end user, (instructions included), or counter-bored at your specified locations by VertiRack, for an upcharge of $40.00. Specify distance to hole centers, in inches, from each end of rail; in the box next to the upcharge below. (example:2",6" = 1st. hole 2" from one end, 2nd. hole 6" from other end) Snaptoggle Kit: Includes steel snap toggles to be inserted into 3/4" dia. holes drilled into truck or trailer body side. The grip range for the snap toggles is 3/8"-2" dependant upon screw length. SELECT SCREW LENGTH / NO CHARGE SUBSTITUTION WITH LADDER RACK ORDER.