Installing a part to help with action from the headstock

[Helbent Revenge]

I don't know what the part is called but it's common on Fender basses, that round part that keeps down the G and D strings:


I'm looking to have something like that but on all strings, and inbetween the nut and first tuner(s), I figure I can tighten it or loosen it and my action through the nut would be adjusted rather than by the bridge. Any suggestions on how I could do this? Here is my bass's head and show where I'd like to install it at:

[Jo6Pak]

Its called a string tree and its not used to adjust anything. It maintains a break angle over the nut to keep tension on it.

[Jaco who?]

The action aka height of the string at the headstock is determined by the nut. Period. There is nothing you can do to change it other than have a different (shallower/deeper) depth to the grooves of the nut.

The round thing is called a string tree. It's purpose is to hold the D and G strings down with similar force as the E and A, which don't need it since their tuners are so much closer to the nut.

Stewart Mcdonald and other parts places sell string trees that brace all four strings, but if you have enough windings going downward from the E and A tuners, they're generally not really neccessary.

[Zooberwerx]

Correct-o-mundo! If the nut is cut properly and strings are wound properly on each post, there should be no need for a string retainer. Your pics are little fuzzy but it appears that the strings may be wound a little too high on each post. This will have an adverse effect on the break angle.

Riis

[RustyAxe]

Everything said here is right on. I would agree that there are too few windings on your strings, causing them to be too high on the post, and the break angle over the nut reduced. I use a rule of thumb when cutting strings ... a tad more than twice the distance between the tuner pegs usually works just fine. And you can cut 'em shorter if you need too, but you CAN'T cut 'em longer ...