I bought a 1992 Fender Squier Korea Jazz bass because it was a cool turquoise color like a '57 chevy but the neck has a large amount of relief. The nut tightens and the relief will get down to about 20 but no matter how much I tighten it does not get lower. The threads do not feel stripped. I took the nut off and put a steel spacer in 1st then the nut and had same result. With the neck off the body using a straight edge I have .12 relief with no tension! I used a clamp and clamped the neck into a backbow situation while tightening the nut but when I release the clamp it goes back. I thought about clamping it in backbow overnight and trying again. I have not reached the end of the tightening but have backed off in fear of snapping the truss rod.Any suggestions?