I'm about to attempt my first ever truss rod adjustment- my TA Sig measures .012 at the 7th and 8th frets. I remove the truss rod cover and here is what I see.
http://farm3.static.flickr.com/2752/4484049729_6939a85fb2.jpg

Now what?

Hard to tell in the pic, but it looks like an allen wrench should fit. Probably metric. Is that just a wood ship in the middle or what?

I haven't adjusted the TRs on my 5120 or 5129, haven't needed it. Hopefully someone else can be of more help.

Hello Likeabrave, did you lay a straight-edge on 1st and 22nd fret? Measure from the TOP of the 8th fret? How is your action now, .012 is'nt that far off. Take a tiny screwdriver and clean out the center cavity, it should be a hex [6-sided] Regards G.G.

You guys are FAST!

Found an allen key in my Allen Key Bucket that worked. I was expecting a hex head inside. Checked the top of the 8th fret - .012 just touched the straight edge. Turned a little clockwise and .010 touches and .008 doesn't.

Thank you for your help!

Make sure the Allen wrench you use fits tightly so as not to round off the corners of the hexagon.

Next, turn the truss rod about a 1/8th turn counter-clockwise to make sure it is free.

Then return the hex nut to your starting point and give it about an 1/8th to a quarter turn, NO MORE!

Wait at least an hour and check your neck relief again. (I like my relief at no more than .002")

If your relief is where you want it, you're done. If you need to take a little more bow out, another 1/8th turn clockwise and repeat the hour wait.

If you have too litlle relief, back the truss rod off a tiny bit (counter-clockwise)