They are made to cover the memory chips on the card, if yours does not already have some. Each bar covers two chips and some have memory on the front and back of the card.
This is my old GeForce4 Ti4200 (back from the dead resently and sitting in one of my LAN party systems). It has smaller heatsinks on each memory chip. My card has them on the front and back, so I had to cut this old Pentium Pro heatsink I got for $1 used at a local shop into 8 small heatsinks with a hack saw. I used Arctic Silver3 with a tiny dab of super glue at each end to attach them. They work pretty good. Here is an old picture (taken with an older Sony digital camcorder).
AMD Phenom II x4 945 3Ghz | ASUS M4A77TD | 2X WD 1TB SATA 2 hard drive | 2x2GB Corsair XMS3 | nVidia GeForce 8800 GTS | ATI TV Wonder Theater Pro 550 | Antec P-160 case | Antec 650w Earth Watts | LG Blu-ray Super Drive | LG DVD RW | Windows 7 Pro