For removing devit, any size
For removing devit, any size does the job.
For blasting designs with finer detail you’ll want finer grit.
If you are sanblasting and then slumping for a matte finish, finer grit will give you a softer, smoother result.
Unless you need to go fine, the coarser stuff is a better value as it lasts longer before breaking down to dust-sized particles.
I generally use 120 as general purpose size – fine enough for most carving, nice finish on matte, and lasts a resonably long time.
Helios Kiln Glass Studio