Why do you need adjustable end links? Well, they allow you to remove any preload from the sway bar. They're not necessarily required with every aftermarket bar, but they are the last step in corner-weighting the car to ensure it's perfectly neutral.
The weakest point in adjustable end links is usually the rod end (or "Heim joint") at the ends. Rod ends allow for a good range of motion and they look like awesome race car parts, but they wear over time. The speed at which they wear depends on the quality of the bearing and the environment in which you live. Some inexpensive ones have a lifespan of 6 months. There's a reason you'll never see rod ends on production cars.
These end links are custom-made for us and feature a strong and durable ball joint at each end. No worries about wear over time! The end link can be adjusted turnbuckle style, without disconnecting either end. Minimum length is approximately 3.125" center to center.
Sold in pairs, which will cover one sway bar. Two pairs are recommended for a complete car. You can use one adjustable and one stock end link per sway bar, but that can make it difficult to reach the additional holes on adjustable sway bars (such as the FM bars). These work well with any sway bar that can use the stock end links, including stock sway bars. Fits either front or rear of the NB and the rear of the NC chassis.
A note on rear NC applications: The fore-aft portion of the sway bar on the rear NC isn't supposed to be horizontal. That portion of the bar should dip down and come back up for fitment / clearance purposes. As long as the sway bar bushing and the top of the end link are roughly the same height off the ground (on level ground), your end link is the correct length. These end links can be adjusted to the correct ride height for most "normal" applications.