Slow blow fuses?

I have been servicing x-ray machines for a long time and have always known slow blow fuses to have a certain look. I have always seen them to be a thin wire wrapped around some sort of foam support or white material within the fuse. I recently ordered some 2 amp slow blow fuses and when I received them they looked quite different. these fuses seem to hjust have a small wire and in the middle of it there looks like a bead of metal. Are these the NEW type of slow blow fuse? Can somebody enlighten me? Thanks