If it's only 1/8 thick it's way to thin to tap. Rule of thumb the minimum depth needs 1-1/2 times the bolt diameter. So a 1/2" bolt needs to be tapped 3/4 inch deep. Machinist/Tool and Die Maker for 37 years. I guarantee it won't hold long in 1/8 thick steel no matter how fine the thread! If clearance for a wrench is a problem look at welding a nut to the back of your bracket and then drilling through the hole. Then you have the strength of the nut and don't need to get a wrench behind the bracket..

 

Thank you. I will use a bolt and nut.

 

Have you thought about mounting it to the rocker box bolt. Rear cylinder right side.

 

After reading the post again I agree.Thought the bracket that was being bolted on was 1/8 thick.
A 1/8 deep hole is too shallow.