i have a 300g-twr and i want to to adjust the truss rod but i don’t know which size it is it looks like a hex wrench but none non of my wrenches worked. help. my guitar has a seriously upbowed neck i just wanna lower the action and keep playing. thanks.
You need a 4mm Allen key to adjust the truss rod.
if i could suggest, when turning the truss rod, do so incrementally. say, 1/8 turn per day until satisfied. also, be aware of creating a buzz on the upper frets if too much is done.
That’s a sensible suggestion, don’t overdo it and take the time to see how the neck settles in after each adjustment.