Factory Exhaust To Aftermarket Muffler Question.

2006 Sierra, said to have 2.75" diameter exhaust. Muffler says inlet is 2.5". I get lost trying to determine ID vs OD of each and what'll fit tightly enough for exhaust clamps.  
 

Is this what I need to mate the two?

Pipe is measured in OD. The only reason you'd specify ID is if you were trying to find something that would slip over it :) You need something that's 2.5" ID and 2.75" ID. Or that thing there and a band clamp.

I'd recommend measuring the pipe on the truck before ordering parts. But yes that sort of adapter should work for what you're trying to do. 

In reply to Keith Tanner :

I think you answered my question, thanks!

And thank you Dylan C. Everything available on line says my factory exhaust is 2.75 so I'm going with that. The internet never lies!

MEASURE.

Generally speaking exhaust systems are 16 gauge, which conveniently is 1/16th of an inch.  So 2 3/4 OD will slip over 2 1/2 ID.

There is one major rule of thumb I have learned about cobbling exhaust together:  Never try to clamp stainless over mild.  It will fail.  Stainless isn't malleable enough to clamp that way.  You can clamp mild over stainless all day long, and it will fail in a year or two at the clamp when it rusts out.

In reply to Knurled. :

Thanks for the input but I'm not using any stainless. Just steel all around.

In reply to ebonyandivory :

OE exhaust is stainless.

In reply to Knurled. :

Gotcha! The amount of rust made it appear steel not (409?) stainless. Thanks!