Part Marking: X100F NZGZ


I am trying to fix a small circuit board that has a surface mount part on it with the following marking:

This part is 5mm (L) x 8mm (W) x 2.5mm (H)

The board was in water so it is hard for me to read the part marking. The part itself looks like a heatsink by its shape, but I’m almost certain it’s not.

There is no part marking on the board that would let me know what this might be, which makes it even more difficult to identify.

Any help identifying this part would be greatly appreciated

Looks a lot like a reset fuse, part number SMD100F. Check them out here.

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Hello rholland,

Welcome to the Digi-Key TechForum.
I agree with slycer2002, that it looks like a resettable fuse, and the X could be the manufacture’s mark.
The problem I’m having is the number on the part looks lke 400F, and I can not find a match to that number.

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Hi slycer2002,

Ordered! Thanks so much!

I’ve been working in the electronic field for 20 years and never set my eyes on a fuse like that. I’ve been at the same company for all 20 of those years and our EE hasn’t ever designed that type of fuse into one of our circuits, so that’s one reason I’ve never seen it. It looked like some sort of heatsink to me, but with no component. Either way, I was lost.

I do some board level repair work on the side and the boards are often 20+ years old or have been fried, so figuring out what components I need to replace can be difficult.

Anyways, thank you very much for answering my question!


Hi David,

Thanks for the reply! I appreciate it.
Yes, under a microscope, I can tell that it is definitely 400F.
I went ahead and ordered one of the parts that slycer recommended. Based on the other compnents on the board that I am trying to repair, the specs on the part that I ordered seem to be in line with the circuit.