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Maxwell Hemmens Caton - fittings thread sizes?

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Martin Lighten30/01/2021 12:25:47
5 forum posts
5 photos

Hi all,

Please could you help, or advise?

I'm trying to find out what the thread sizes are on the two Caton steam engines I have. I am in the process of installing one and realised these are not standard ME threads on the displacement lubricators; for both the engine connection and the pipe connection.

Caton 1 exhaust fitting removed.jpg

Also I want to pipe away from the exhaust ports with copper not rubber. So Caton 1 (above) has a threaded fitting which unscrews, but again not sure what the thread size is. Caton 2 (below) has an exhaust port but it is not threaded, so what was used was it a fitting that was just push fit?

Caton 2 exhaust port.jpg

I think there is probably some evolution between the two engines as the engineering is different. But I'm sure they share the same heritage.

Hopefully that is enough information to answer the questions, but if you need more please let me know. Thanks in advance.


David Marks 131/01/2021 11:41:11
255 forum posts
44 photos

Do you have a means of checking the thread outside diameter and pitch.? The threads are possibly BSP.

Richard Simpson31/01/2021 12:22:21
308 forum posts
141 photos

Hemmens usually uses a 40 tpi thread of varying diameters. You should be able to purchase fittings from the usual steam suppliers knowing it is a 40 tpi thread and measuring the outside diameter in inches.

"Steam Fittings" for instance supply 40 tpi threads.


If you still have trouble contact John Hemmens through his website, I'm sure he will be able to specifically identify every fitting.


Edited By Richard Simpson on 31/01/2021 12:23:37

Martin Lighten31/01/2021 12:35:11
5 forum posts
5 photos

Hi David, Richard,

Many thanks for your responses. I have measured the outside diameter on the oiler, which is 5.9mm for the pipe fitting and 5.2mm for the engine thread on Caton 1. But I don't have a means of measuring the pitch. The Caton 2 oiler threads are the same for the pipe fitting 5.9mm and the engine thread is smaller at 3.5mm? I'll get the nearest inch equivalent.

I have a stack of standard ME fittings for the pipework, but the engines threads are smaller and possible a different pitch?

I've now seen from another post on Model Boat Mayhem that the thread for the pipe fitting may be A/F? See the two posts below:


Hi, Max Hemmens Caton engine threads, are just slightly smaller than todays std of 1/4 by 40 tpi, don't try and force a todays std union nut, or you will strip the threads,!!!


Hi, I have just checked my old books, and Max Hemmens Caton engine, union threads are A/F and not to day sstd ME


So I don't know if that helps. I've tried contacting Roy who posted the two answers above but I'm not sure if I have the right email address.

If I can help more please let me know.


Martin Lighten31/01/2021 12:43:35
5 forum posts
5 photos


Thanks for your advice, always welcome. It seems eons since we last spoke at IMBS.smiley

I will contact John Hemmens and see if he can help.


Richard Simpson31/01/2021 13:35:19
308 forum posts
141 photos


For some reason or another everything seems to have been a lifetime ago nowadays! If you can get your hands on a thread gauge they are well worth having around. Mine cost me around a fiver so you can't go wrong really but make sure it includes a 26, 32 and 40 tpi gauge as those are possibly the most likely ones you will come across in steam models.

All the best


Martin Lighten31/01/2021 15:05:41
5 forum posts
5 photos

Thanks Richard.

I'm shopping for one now.


David Marks 101/02/2021 15:01:49
255 forum posts
44 photos

Martin - Having converted your metric diameters to imperial, all the sizes are too small to be BSP at least in the Zeus tables the smallest recorded is 1/8 BSP 0.383 inch which is 9.7mm. There is a possibility the threads are BA, in descending size order 0BA, 1 BA and 4 BA. From thread tables that I have, the corresponding Major Diameters are 6.0, 5.3 and 3.6. If you would like to send me your email address via a PM on here I will supply you with a document which I prepared for my local model boat club entitled Thread Identification. This has info diameters, pitches etc for the BA range.

Martin Lighten02/02/2021 07:41:13
5 forum posts
5 photos

Hi David,

Thanks for the research I’ll PM you now. I’ve been looking at tutorials online and reading articles on thread sizes, and I must admit there are more ‘standard’ threads than IT operating systems. laugh

All of them I’m sure have their uses, but what a minefield for the uninitiated when you enter that world. You probably spent the first year of your apprenticeship learning them all. I was quite happy dealing with ¼ x 40, ¼ x 32 ME, but even that was created from another ‘standard’.

The British Model Engineer Thread is based on the Whitworth thread with a pitch of 32 and 40 TPI. A commercial use of this standard does not exist.
The flank angle is 55°.

John Hemmens has kindly responded as well, and will hopefully follow up on his initial contact.

My thread gauge is ordered. But I suspect like a lot of tools, it’s how skilled you are using it that counts. A bit like Harry Potter’s wand.

Thanks again David.


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