I should mention that this is all to make it easy to screw on and off the heatsink in a similar way as you would on a CPU.
If you don't care about that and only plan to mount it once, you can just use a 6-32 1.5" screw and nut to hold the heatsink down. You can still even use the spring if you want. They're just a more of a PITA to install that way, especially if you take them on or off. Also, make sure you keep the springs and that little clip somewhere safe so you can put it back on later when you move the HS to your new 50PH/s Intel ASIC machine in early 2015 when BTC hits USD$5000.
If you don't care about that and only plan to mount it once, you can just use a 6-32 1.5" screw and nut to hold the heatsink down. You can still even use the spring if you want. They're just a more of a PITA to install that way, especially if you take them on or off. Also, make sure you keep the springs and that little clip somewhere safe so you can put it back on later when you move the HS to your new 50PH/s Intel ASIC machine in early 2015 when BTC hits USD$5000.