The difference between large bead and small bead on the 1966 Canadian silver dollar?

The way to tell the difference is as follows:

The "beads" that are being referred to on this coin are the beads that circle the outside rim of the heads (obverse) side of the coin.

Small Beads Variety - On the right side of the queens face is the inscription D.G. Regina. If you take a close look at the periods after the "D" and the "G" of this inscription and compare their size to the size of the beads, the beads are noticeably smaller than the periods after the "D" and the "G".

Large Beads Variety - In this variety, the beads surrounding the rim are at least the same size or larger than the periods after the "D" and "G".

If you do have a small beads variety its extremely rare and is worth anywhere from $1,300 to $7,300 depending on the condition and strike of the coin.