Please correct me if I am wrong.
IIRC;
Tubing and collector material is 304 grade stainless steel, polished, no coating, 1.625" outside diameter tubing on the primaries. Estimated primary lengths range from apx 14" shortest to 22" longest.
Head flanges appear to be 3/8" and also be of 304 stainless steel (some headers use mild steel flanges even with stainless primary pipes)
Downpipe flanges appear to be 1/4" inch and also 304 stainless steel.
This is a great price compared to any USA manufactured stainless headers.
BTW, the collectors used are ok but for someone wanting to improve the torque range merge collectors would be better. This of course would require the expense and fabrication to either buy or build merge collectors as well as cutting the existing ones off and welding on new ones. Of course doing so would void any warranty.
Here is a company that makes very affordable formed collectors that are 9/10s as effective as a fabricated merge. Nice option.
http://www.coneeng.com/collectors.html
The formed outer cone is about $60 ea in 304 stainless
The inside "bullet" kit is about $50 ea fully welded in 304 ss.
construction image