We can supply Brass hollow Rods in Multiple Diameters, Wall Thickness, lengths, and Finishes.   

Diameters available :  3/8" ,  1/2" , 5/8" , 3/4" , 1" , 1 1/4" , 1 1/2" and 2"

Lengths available :  6'-0" and 12'-0"  we can cut these to sizes as per your measurements

Thickness available:  0.040 mm (1/24") (standard) , 0.062 mm (1 /16") (thicker) , and 0.125 mm ( 1/8") (thickest)

Finishes:  Polished Brass, Polished Chrome, Polished Nickel, Satin Brass, Satin Nickel, Antique Brass, Oil Rubbed Bronze, Aged Brass, Un-Lacquered Polished Brass, Black Painted un-lacquered, and Dual Tone Finishes

Most People use 1 1/4" Diameter Rods for their Closets Rods, these work best for standard clothes hangers.  1" or 1 1/2" diameter work fine as well.  

Picking the right Diameter and Wall Thickness has to do with the span of the opening, brackets used for mounting, mounting of the hardware to the wall, weight of clothes expected, is some sagging acceptable, and the desired look you are trying to achieve.  

Guideline recommendations for 1 1/4" D Tubing's, Your designer and contractor should make decisions per the project requirements.  

1)  0.040 MM Standard rods should be supported at every 2 to 2 1/2 feet by center brackets

2)  0.062 MM Thicker rods should be supported at every 3 to 3 1/2 feet by center brackets

3)  0.125 MM Standard rods should be supported at every 4 1/2 to 5 feet by center brackets