the pryamids are very good i think they come in different sizes
7/16 means they have a slot in the bottom to fit 7/16 slats or cross members on your burn table.\
you can get with single slots or double like an x or +
you can position them under your plate not to burn them but you still can't help from burning some of them.
makes your cross members last a lot longer.
the size of the slot on bottom will determend how much they wobble
most of them fit realy good.