Suppressors Checking barrel thread alignment?

I know someone sells rods in rifle calibers that you put down through the can and into the barrel to check alignment. Not sure who, but when I bought my can, the shop had some on hand and checked it for me.

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I have been happy with them. The .223 rod I received might have a bit of a bend in it, or some threads are off.... Larger diameter rods have been good. For the price they are good enough/better than nothing. The .223 does slip into a .22 LR bore as well.