The biscuits can be adjusted to fit whatever size shaft you are using. If you need to make the hole smaller, take the biscuit out and squeeze it together. You can clip a bit off the metal ring if you need to go smaller than normal.

When I trim my biscuits, I trim a bit less off the bottom of the biscuit. My vanes are positioned so they do not go through this portion. I haven't noticed anything negative with arrow flight, having done this.