This listing is for a "self lubricating" bearing / sleeve / bushing / whatchmacallit, these are brass with graphite inserts.
These bushings are the same dimensions as the common linear roller bearing LM8UU which is common, on 3d printers, 8x15x24mm
The only difference, apart from not having balls and so running smoother, quieter, and not damaging your rod, is that these don’t have the mounting grooves at either end that LM8UU do so you might have to think about mounting/clamping.
8mm ID, 15mm OD and 24mm Long
