Confused about BSP thread size

[pophops]

Hi. I'm a new member so please be gentle with me!
I have a narrowboat and have been experiencing some problems with the exhaust leaking fumes.
I have fitted a new flexible coupling because the old bellows had split but now find that the silencer has rusted through and needs replacing.
I need to identify the correct thread so I can order the right silencer. I've undone the unions at each end but it's difficult to measure exactly the diameter of the threads in the confines of the engine hole and the silencer bracket is rusted solid so I'll need to do some more work before I can remove it..
The thread diameter on each end of the silencer appears to be around 2 1/4" (57mm) - difficult to be precise. The confusion arises because the nuts on both unions are stamped 1 1/4" on one of the flats and incidentally are stamped 'GC' on another. the nuts measure approx. 2 5/8" across the flats.
Could anyone identify for me what size of fittings these are?
Thanks for any replies.

 

[Chalked]

Very likely to be BSP on a boat.

 

[Riley]

Welcome along mate, you only need to post once as the moderators may see this as spam

 

[snowhead]

The threads would be 2" ;
[DLMURL]http://www.floconfilters.com/images/bsp_new.jpg[/DLMURL]

GC may be Gas Council possibly a gas approved fitting.

1 1/4" doesn't make sense

How old is the boat?

 

[pophops]

Very likely to be BSP on a boat.

Thanks but what size BSP?

 

[quality]

[url]http://www.newmantools.com/index.html
Have a look at bsp tap sizes
[/URL]

 

[rpm]

If your narrowboat is as old as the one my sisters lives on then it could be any thread, reckon over the years we`ve found every imperial and metric threads known to man.

Do Halfords still sell those dunk in water and wrap around exhaust repair kits?

 

[rpm]

Stationary Engine Parts Ltd
Or
Zeus Precision Data charts and reference tables on fleabay for around £6

Zeus Precision Engineers Metric Data Book Chart Charts Reference Sizes Tables | eBay

 

[Dotty]

Welcome along mate, you only need to post once as the moderators may see this as spam

We take a very dim view.

OP. Please don't do it again!