The diamond on these glass bits is much finer grain than the diamond on the "new stone bits" this same company has for sale. This is a nice quality bit, and it is made for shallow drilling in glass (about 40mm or 1.5" working depth). The fine diamond will be less aggressive in cutting but produce a very smooth hole. I will be drilling in hard stone, and in the future I will reorder the stone drill bits, which are more suitable for my purpose.
This core drill bit has an excellent quality!