In the novarossi world yes, H means cold.

Picco although Italian, TH means the short bodied hot plug. www.nitrohouse.com is a great place to get picco plugs and they show the package, the 6tc says cold on it.

I run the IDM variant but I imagine it is the same for all, I run the 6TH (or IDM6) everywhere all the time in the 12 evo3 and evo4. I run the 7TH (or IDM7) in the 21 for onroad and a 5TC (IDM5something odd) for offroad.

I don't believe in changing glow plugs even from when I break an engine in, with the 12 evo3 I usually go through 3-4 rods before the plug eventually pops. The evo4 I'm told has a superior rod so I guess it will go 3-4 gallons before the plug pops and it will eventually but I haven't had it happen so I don't know as I am still on the same plug with 2 gallons from nationals.