Here is my answer for a replacement radiator fan switch used in our MK IVs.
My one let me alone after the first engine start this year and i went hunting for donor car and part.
Finally i ordered a switch which is exactly the same but different number on it.
The MK IV switch is a Otter switch # 5802082
The switch i found with the same dimensions and switching temperatures is out of a MGB from 1979 on with # 6800057A, maybe other switch manufaturers have different part#
Don't forget to order 2 rubber grommets with the switch, one for installation plus one spare part.
Don't reuse the rubber grommet because the radiator cuts into it forming a good seal during the installation.
Install the grommet first, add some water to the switch and grommet and push it in position by hand.
Everything fits perfectly.
The part can be found for example at
www.mgpartsuk.co.uk and other shops.
Here a direct link:
https://www.mgpartsuk.co.uk/store/index.php?route=product/product&path=330_304_243&product_id=5359 Happy motoring, Uwe
Original part and grommet on the right, replacement and grommet on the left.
Even if the dimensions look different because of the photo angle they are absolutely the same