OneGuyFromBarlick

I thought China was going to be about right - that it provided an extra circle of foundations.

On the other hand, being in a river valley, was it to protect the chimney from flooding that would compromise the foundations?

Ah! At the last minute an answer close enough to qualify emerges. Yes, Peter I'll take that one. The foundation of a chimney like this is a circular stone pad about twice the diameter of the bottom of the stack and that is built up by successive layers of brickwork which reduce by about a course a layer and this continues until it is the diameter of the bottom of the stack. Normally this point is at ground level but this stack is built in river bottom silt and the object was to make sure the stone base wasn't below the water table as if it was any slight movement pumped water and eventually the stack tilted. Raising it like this meant the top courses of the brick foundation were exposed, in fact they almost reach the top of the roof. We found that when we were repairing the slates. So it is nothing more than a protective cover for the foundations. You were so close China but not quite there....
Next for shaving?

What is it?

I think I know but I'll keep quiet for a while.

Thank God for that. Good lad China!

A dummy for an engineer's baby?

A grease nipple?

Sorry, nobody is anywhere near yet.

Boiler safety valve. Usually kept in a drawer for safety.

A press stud?

In a way you're right Ken but not as you mean it.
Sorry Gloria no.
Clue, follow Ken's lead and concentrate on boiler safety.
(Is this going in the direction you expected China?)

It has a look of the pressure release thingy on a pressure cooker.

Pressure relief for a compressor?

You're all drifting away from the answer. Boiler safety You're almost there.

Something to do with gas boilers?

This is one of the mystery objects that takes me by surprise. I thought you'd get it right away.
China, you'd better tell us what you think it is. If it's not solved by lunchtime I'll knock it on the head.

Is it one of those valves that melts if the temperature gets too high?

China will not be happy! Yes Peter it's a fusible plug. This is a big one for a Lancashire boiler furnace tube, one in the crown of each tube. If the water level falls the plug gets hot enough to melt its core and what steam and water there is in the boiler blows into the tube, extinguishing the fire and warning the attendant he is in trouble. See THIS Wiki article for more detail.
See THISarticle on the site in Steam and waterwheels.
Next one?

Stanley wrote: ↑07 Dec 2020, 09:03 In a way you're right Ken but not as you mean it.
Sorry Gloria no.
Clue, follow Ken's lead and concentrate on boiler safety.
(Is this going in the direction you expected China?)

Yes. I know! [smug]

Would 2-inch thread be a clue?

Sorry, didn't see the post above.

I thought you'd be pissed off because Peter popped in with the answer which I was sure you knew. I shall think of another one, watch this space.

Mrs Tiz has just told me I should have identified that straight away because we have one on the outside wall of our kitchen wall!

What is it and where?

Peter, that sounds interesting, send a pic. Can't understand how your kitchen wall got a fusible plug.

No takers? I can knock it on the head if you like.

I think I have seen this before but can't remember the story. A floating double deck shed!

Good man China... Keep at it. If you get stuck I can give clues.