Cast iron radiator fittings

[notgreat]

Hi all
I am converting a 1910 community hall. It has 3 original cast iron radiators which are in good order but were installed via big steel pipe. The radiator fittings (connectors) are a big problem. At one end I have a steel pipe coming out with a 14tpi three quarter BSP tapered thread, that's no problem, but at the other end is a female fitting which is the size of 1" BSP but is a 14tpi thread (BSP 1" should be 11tpi). I have a T piece which has the same threads (extracted from elsewhere in the system) and measurements are male od 33mm, 14tpi. What fitting is this?? I have so far baffled all the plumbers merchants in the north east as the T piece has 2 female which are 3/4 bsp and then the male which is not bsp and its the 'male not bsp' that I need. There are also some elbows which have the same 14tpi thread and 33mm size.
All help appreciated as the radiators are original so keeping them is important (it's also a listed building and until I disconnected the system they worked very well!)

 

[gmartine]

I thought it might have been 1 1/4 UNF but I couldn't match the OD (31.7mm), I've seen some fittings (non plumbing) as well as taps and dies that claim to be BSP 14tpi so I think it might actually exist. You might be able to pad out the above UNF to fit but it's too specialist for merchants, my next enquiry would be to radiator specialist/refurbishers or a machine shop to have a fitting made.

 

[ShaunCorbs]

Sounds like a one pipe system

Threads will be npt and going off your sizing one side will be 1/2 eg 15mm and the other 3/4 eg 22mm

 

[chris watkins]

Up until that sort of time there was an 1 1/8" BSP, I wonder if it is that?
I had a set of pillar taps that size once & had to get a pair of brass FI to 22mm comp adapters made by Barber Willson, cost me a lot of money.
It sounds more like a Rad union thread, what dose it connect onto ?
Photo would be helpful.

 

[notgreat]

Thanks for the replies. Unfortunately it isn't npt, wrong tpi for size. OD is 33mm (inch and a quarter) and is bang on for 1"bsp but the thread is wrong. They used to connect in to a one pipe system with one and a half inch steel pipe. I do have a couple of elbows which have the odd thread male fitting at one end and bsp at the other, I could use them for one rad but what about the other two?
Reckon I'll end up trying to find a small machine shop that will knock something out for me.