The thread appears to be 26 tpi (whitworth), with an outside diameter across the threads of 0.495inch. I have determined this using a thread gauge, but there isn't an awful lot of thread to work with on the steam pipe and even less on the cylinder.
I was hoping to cross check my findings against the Spink drawing, but unfortunately this shows a flange joint onto the cylinder from the steam pipe.
Hi Paul, The exhaust on my Brit is much larger, either an imperial 3/4" 16tpi(it could be a unf thread) or a metric size (19mm). Unfortunately I don't have a thread gauge to check the pitch. I have built a new blast pipe and blower ring and want to mount this onto the pipe, as it's screwed on I can adjust the choke distance between the blast pipe tip and the peticote.
I believe there are lots of similarities with the 9F so just been out to check mine. Unfortunately it's tucked in the corner of the shed so I couldn't reach the front end and I can't pull it out without help. If you haven't got an answer in the next few days then I'll see what I can do but it'll be next Friday at the earliest.
Winsons certainly used some odd threads in some places - the adapters I made to connect an airline to the threads in the smokebox were 5/8 x 26tpi which I think is Cycle thread. I think from memory I also came across metric in some areas.
I think I have been barking up the wrong tree here. To try and clarify I will add some pictures (when I can remember how to do it). The thread size I described previously was the STEAM INLET connection to the cylinder. On the back of my cylinders there is a machined slot that is the exhaust port. There is a cylinder mounting plate bolted to the cylinder casting which is in turn bolted to the frames. On the inside of the frames there is then a bolted manifold which goes to the exhaust ring. Is this different to yours?
Hello cplmickey Lovely photos! Yes that big thread was the one I was enquiring about, the Brit cylinders are machined in exactly the same way as your 9F. I must have a go at uploading some pictures as I've also modified the ashpan with 3 drop down doors and a removable side so that the grate can be removed without having to take the boiler off.