I bought the ones which end "EGT" by mistake. Take care they are very similar.
OK ignore some of the above. The original thermocouple & display work perfectly it was the transformer that was wrong - It must be a DC one & the link above is for a halogen light and won't work - see below post for the correct one - modified 25/6/12
Those thermocouples are the same as I got, they are a lot bigger than the picture on ebay would make you think... the probe is about 1cm in diameter so not really one to squeeze between your floor bricks... The cable is very long though, so I have cut one of them into smaller cables. Thermocuples are all about the join between the two types of metal so as long as you have a good tight twist at the end, you have a thermocouple, a weld of some kind would be better, but for experimental purposes... :-)
The 2 different metal wires will be welded to the inside of the end of the probe, so if you are talking about the large ones from hk... I would make it flush... the end face is probably as sensitive to temp as the outer edge... test is with a lighter and see which part of the probe causes the biggest jump in temp... it should be the very end..
Personally, I wouldn't have the thermocouple directly exposed to the oven interior, as it may suffer from corrosion. Bedding it into a brick or the mortar say 10mm behind the face would seem better to me. It should still respond fairly quickly to temperature changes within the oven and there shouldn't be too much lag.
I give in - the e-bay link didn't work - try typing in "Philips Mains Adapter 12v 50mA Output DC Plug" into google - its some sort of digibox power supply.
I've cut the end off & it works a treat. I'm not sure exactly how to keep them waterproof though.
I thought I would cheat & only bought one transformer and ran a wire in parallel from one to the other. I should have paid more attention in physics class because that doesn't work. You need one transformer (ie. plug) per display. At the price it won't break the bank.
24degrees C. isn't far off & when I waved my weed burner inside the oven it was straight up to 90 or so.
So in a nutshell both the original thermocouples and the displays work perfectly. It was the transformer I bought that was wrong. The displays are a bit fussy but having got the correct transformer - happy days.