[DonRotolo]

If you are using spacers to offset the sprocket, the larger the outside diameter of the spacer the more it will resist bending (and thus shear on the fastener) forces. The hex spacer is not better if it is the same effective diameter as a round spacer. The 'ideal' (for strength) would be a complete ring with holes drilled for the fasteners.

Adding some kind of surface feature as Tom Line mentioned would further put the stresses onto components that can handle it (i.e., not fasteners) because, as Tom also mentioned, #10 hardware is far better in tension than shear.