Use pipe die on worn threads if you have enough room for die to fit. If not, clean threads with wire brush.
If it is "rusted out" you do not repair it, You do replace it with XHCI
Because threading thin wall pipe renders the pressure rating ineffective, as it thins the wall to much to be able to withstand the pressure.
I know that it is usually suffcient to just glue it,just make sure your mesurements are on point, but if you must be anal use sheilds and screw. Either or. joe hojas
npt, national pipe thread, is a standard for threads on a screw. I (not a plumber) don't believe "npt valve" makes sense , but probably refers to a valve which has npt threading. Yes, a NPT Valve would be a valve with pipe threads as opposed to a sweat valve which has solder connections. There are several other type of piping connections too.
Are you starting on the right side of the die? It does make a difference. Usually the side with the size or name on it is the side you start with.
Rusted cast iron.
If it is "rusted out" you do not repair it, You do replace it with XHCI
Hacksaw
Remove the heat shield (if there is one) locate the set screw hole, remove the old baffle (if there is one) insert the new baffle with the screw hole mating up with the pipe hole, add a lil' blue locktite to screw, and screw it into the baffle through the pipe. Re-attach heat shield (if there was one removed). If baffle is a quite one with fiberglass wrapping...leave it on.
Remove the heat shield (if there is one) locate the set screw hole, remove the old baffle (if there is one) insert the new baffle with the screw hole mating up with the pipe hole, add a lil' blue locktite to screw, and screw it into the baffle through the pipe. Re-attach heat shield (if there was one removed). If baffle is a quite one with fiberglass wrapping...leave it on.
There are instances when corrosion occurs at the junction of a carbon steel pipe and a brass valve. This is often the result of a pipe threading failure.
There is an internal pipe wrench that goes inside the pipe and expands as you turn it and it turns out the broken piece. You should be able to get the tool at a hardware store.
I'm confused by your use of the term, center to center. I'm guessing you mean from the face of the fitting where the pipe threads in. You can usually screw in about 1/2 inch of pipe into a female fitting, so you would need 10 inches to end up with 9 in between. You can screw this together without a union in between? You can only put pipe together in one direction unless you use a union.
You should see a horizontal steel pipe just in front of the engine. This pipe has the bleeder screw.
Because threading thin wall pipe renders the pressure rating ineffective, as it thins the wall to much to be able to withstand the pressure.
With a stock and dies and a pipe vice or a threading machine such as a ridgid 300 or 400 or a 12 R or a 65 R depending on the pipe diameter and do not forget the oiler One can always use an Armstrong stockThere are many ways to thread pipe the most popular way is by thread dies of standard pipe but many other ways by using a lathe or cnc machines.When threading pipe of usually 1/2 - 2" standard pipe threads you must use the right threading oil because other different oils will damage your dies so if you are renting or borrowing a threading machine please make sure you have the right threading oil and the more oil you use while threading the pipe the longer your dies will last.
I know that it is usually suffcient to just glue it,just make sure your mesurements are on point, but if you must be anal use sheilds and screw. Either or. joe hojas