I could be wrong, but I think:
All the new GGTSs and Stealths comes with brass positive center pin.
SS GGTS (and Stealth) comes with brass button top.
Button's spring, housing and plunger are brass.
GGTS's and Stealth's axis (bottom cap post) and battery spring is brass (with a brass fuse kit option, sold separately).
The GGTS included reathreders are used to convert the default GGTS connector threads (510) to 901 threads, it is not an adapter, it is a reathreder, adapters have a center pin, the GGTS reathreders doesn't, because GGTS has an auto adjustable center pin. Those reathreders are useful if you want to use normal 901 atomizers or to combine with chinese adapters to use big atomizers on the GGTS, but the GG GGTS adapter is the best method to do that:
http://ggwiki.et.com.mx/index.php/GG_adapters
I'm unsure if the new GG brass alloy is used for parts as the positive center pin, button head, button housing, button pin, and axis.
Imeo makes optional GGTS's brass big parts (telescope tube, bottom cap, extension, main tube, etc.) so you can have a full brass GGTS or a SS GGTS with brass accents or a brass GGTS with SS accents and, for example, sometimes re sellers have special editions with brass and ss combination (as the GGTS COV edition).
