Seamless DOM Tubing 

DOM (drawn over mandrel) round seamless tubing is made by cold drawing a tube through a solid steel mold (mandrel). In the process the OD and ID of the tubing is kept to much closer tolerance than hot rolled or electric welded tubing. 

There is no inner seam in seamless tubing. The drawing process also work hardens the surface of the tubing making it stronger. 

What about chromemoly tubing? It is a different alloy than mild steel and contains some chrome and manganese. At the same strength level chromemoly weighs about 25% less than mild steel. Therefore chromemoly is the perfect choice where weight is a major concern like aircraft or auto racing.  

Chromemoly has a serious drawback for use in most metal fabrications, however. It is very brittle and can stress crack easily if not carefully TIG welded and stress releived after welding. For most people  the weight savings is not important and they don't have the equipment or skills to use chromemoly.

So use DOM tubing. Unless you are building an F14 jet or an INDY race car (NASCAR specs DOM!) live with the 25% extra weight. Weld it with any process you choose. Be happy,  safe and save about 50% compared to chromemoly.

Seamless Mild Steel Tubing

1020 DOM