The Vantech H3 3 bar rack system with Endcaps is a clamp-on system requires no drilling for installation. The system clamps onto the existing drip/gutter rails. The cross bars are 3 x 1.5 heavy duty reinforced extruded aluminum. Cross bars have built-in channels for additional accessories (Accessories such as A03 Side Support, A57 Adjustable Ladder Stoppers, A64 Push to Secure or A69 hook & loop Strap. Not Included). The mounting bases are aluminum at 3mm thick and 8 wide for better support and grip. The H3 system has a clearance of 11 from the drip rails to top of side support. 2X 3/4 Eyehooks are located on each mount. It is also galvanized then dipped in rubber for additional protection.
See here for more pictures and information: https://vantech.us/product/aluminum-h3-system-with-acc-for-a-ford-econoline-1992-on/