Here is a Basic Spec Sheet of the Materials and Size of Tubing/Mufflers. 

Aluminized Steel- Steel With Galvanized Coating

Tubing 16 Gauge

1-3/4 Inch O.D.

2 Inch O.D.

 

Tubing 14 Gauge

2-1/4 Inch O.D.

2-1/4 Inch O.D.

 

Mufflers (Aluminized)

20 Gauge

 

Stainless Steel

Tubing- 304 Stainless Steel 14 Gauge

1-3/4 Inch O.D.

2 Inch O.D.

2-1/4 Inch O.D.

2-1/2 Inch O.D.

 

Mufflers- 409 Stainless Steel 

18 Gauge