how do the EVO lower control arms hold their length?

I'm stuck between the Currie and EVO front lower arms. I like that the Evo's can be adjusted on the jeep, but I'm not sure how they hold their adjusted length? Is the inside of the control arm smooth, and clamps to the threaded johnny joint? That seems like it could slip. The currie is a direct thread connection, but has to be dropped out to adjust.

I want to play around with castor to see if I can improve my 75mph highway handling a bit. She moves around a bit at 4deg castor. I'm never adjusting my rock krawler arms again, they're going up for sale. I want to try 6 and 8 degrees to see how it changes.

Collar threads into the arm, Joint threads into the collar. Adjust collar for length, clamp down with the bolt on top.

Perfect thanks. From the web pics that collar just looks like a nut.