Czech size 6/0 seed beads with the unique etched finish, sold in 10g bags (approx. 190 beads); 4mm in length, 2.4mm in width, hole size is approx. 2mm.
These are smaller in width (hole-to-hole) than Toho (2.7mm width) & Miyuki (3.1mm width) 6/0 beads; if it’s important that your 6/0s line up exactly, you may want to stick with one brand.
The non-etched Czech 6/0 seed beads have a slightly smaller hole (approx. 1.5mm). Measurements are as above but, because these weigh more, the quantity per 10g bag is approximately 150 beads.