What is this odd addition to mains transformer?

[retailer]

I'm gradually selling off unwanted gear and I came across this mains transformer with an odd addition, the 'hook' is connected to the LH side terminal (with the red wire) by a short section of wire - the hook is fixed and can't move, the spring does not hold a great deal of tension, it is easily unhooked, has anyone come across this sort of thing before, the only explanation I can think of is a sort of crude over temperature disconnect - where the spring has current flowing through it - too much current heats the spring it expands and loses contact.

[snowman_al]

Is it from something made by Philips?
I agree its a thermal fuse, but suspect there is a low melting point joint internally that releases a connection when over heated and the spring pulls it open?

[Refugee]

It looks Phillips to me too.
It is missing the "U" shaped bit with the low melt solder in it.
The hooked bar is supposed to conduct the heat from the overheating transformer windings to the solder blob in the "U" shaped bit allowing the spring to pull the power off.

[retailer]

Thanks for the prompt replies, it looks as if part of the thermal overload is missing I'll probably just bypass for testing