Weve all heard it, that THUNK ,THUNK sound every time you move your doll or even just pat her ass as you go by THUNK< THUNK caused by the screw joint in the neck being to loose letting their head wobble from side to side.
Not being one for a Bobble Head doll I set out to fix this and below is what I devised and use on all my dolls.
M-16 HEAD BOLT MOUNT
I start with 2, 1/2 inch flat washers (13mm) a medium resistance coil spring11/4 inches(32mm) long (20mm inside dimension)

Drilled the center hole of the washers out to 11/16 (17mm) sanded all rough edges smooth.
wrapped the neck bolt in teflon tape,insert bolt into the neck and assembled the washers with the spring in between them.

Push down on the top washer to compress and started screwing the head on CAUTION! make sure at this point you dont cross thread the head. Once head side is started I rotate until it goes completely tight and then readjust her head facing forward.
I also discovered that she now has a very smooth head rotation and when I position her head for a pose and let go it doesnt fly half way back around . Hopefuly this will be of use to some.