Gunsmithing Surefire brake install... chamfered spacer needed?

[Johnson184]

Looking to install a surefire brake onto my AI’s 5/8x24 threaded barrel so I can use my SOCOM suppressors. Kit looks like it comes with shims and a chamfered spacer. Do I actually need to use this spacer? I understand why it’s needed for something like a SCAR17 with a limited shoulder, but for something cut as precisely as an AI barrel, is it needed?

 

[Gasgun]

That spacer is for use on barrels without a relief cut in the threads at the shoulder.
It has nothing to do with the accuracy of the threading.
This is mentioned in the mounting instructions.