I've just had to reset the thermal cutout of my immersion heater. Whilst removing the cover, I've stupidly dropped the nut somewhere behind the tank. Fishing around with a magnet has pulled up all sorts of metal objects, but unfortunately not the nut.

Photo of the screw/bolt

The long threaded screw/bolt in the above picture goes through the hole in the cap. The nut then secures the cap in place.

The cap, with the hole the screw/bolt goes through

Will this screw (or threaded bolt, I suppose) normally be a standard size? If I were to try and buy a replacement, what should I be searching for? Or will I have to get hold of some calipers and measure the darn thing?

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    May be metric or BA if you have a few spare nuts in the ofds and ends jar then test. – Solar Mike Jul 11 '20 at 10:29
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    on the other hand, there may be another reader here who has the same heater and set of test nuts, – Jasen Jul 11 '20 at 11:29
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    If you have the screw, take it to a hardware store and find the mate. – Hot Licks Jul 11 '20 at 18:29
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    @HotLicks Sadly it's fixed to the heater. Good idea though! – Tom Wright Jul 11 '20 at 19:20
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    @PeteKirkham - I should have known that! I have a couple of those toolholders. – Brian Drummond Jul 12 '20 at 11:41

There's no reason it would not be a locally standard size (given a British location based on the label, presumably metric or pre-metric British Standard threading) so some basic measurements (no calipers required, if you are willing to use a ruler carefully and buy 2 or 3 nuts, one of which will be the right one) and a trip to the hardware store should find a nut to fit.

You might also try putting fine net mesh over a vacuum cleaner inlet and vacuuming for the nut, first.

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    Thanks Ecnerwal. The vacuum cleaner tip is a good one, but the space is (alas) too confined. I'll use a ruler and see what my local Screwfix has available. – Tom Wright Jul 11 '20 at 16:53
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    @TomWright I sometimes tape a drinking straw to my vacuum in order to reach a small nook or something small that needs cleaning. Might that work? – Tim Jul 12 '20 at 10:14
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    Thanks @Ecnerwal - it turned out to be an "M5" (5mm dia) metric bolt. – Tom Wright Jul 14 '20 at 12:50

Dab a light coating of any oil on the outermost cm of the screw. Mix up a very small quantity of epoxy putty and form it into a nut-like ring on the oily threads near the end of the screw. It doesn't need to be hexagonal. When the epoxy hardens, unscrew it from the screw. Replace the cover and install your epoxy nut.

  • Ingenious! If only I had some epoxy to hand... – Tom Wright Jul 11 '20 at 19:22
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    @TomWright - If you get it on your hand it makes a mess!! – Hot Licks Jul 12 '20 at 16:37

Standard screws for fixing faceplates etc is M3.5.

tbh that could be anything - but looking at it I'd guess M5?

If you've an engineering supplies place near you then you'll get a handfull of nuts for under £1, screwfix tend not to be any good for 1 or 2 item

  • Based on the answer from Ecnerwal I measured it and I think it's either an M4 or M5, yeah. Good tip re Screwfix - looks like I'd be spending 8 quid on 2 boxes of 100 (one in each size)... – Tom Wright Jul 11 '20 at 19:23
  • You were right, by the way - it was an M5. – Tom Wright Jul 14 '20 at 12:49

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