This is a standard sized glass fuse like what cars used before the 80s. I can faintly make out 20A, but I’m not sure what to call it in order to find a replacement. The fuse in the picture has not blown, but it is the only one I have. I don’t think it matters, but this happens to protect a transformer for a pool salt generator.
I’m also interested in what purpose the spring serves. I’m sure I can find another 20A fuse, but I’m not sure I can find one exactly like this, so I’d like to know why it is special.