Hey master's, I need help. Like an idiot I tried to use the old head bolts to save money and broke one. I was able to get it out and the threads were rough so I found out they are 1/2 inch so I tapped the hole with a 1/2 tap. I am using new bolts this time but the tapped hole just spins as soon as I put a load on it. Please Help, Scott.............................:confused :

 

They're not 1/2" bolts, but M12.