These are sold separately!

These are a simple way to adjust chain line.
Precision alloy washers made to specific thickness; by adding one or more to each bolt between the crank and the chainwheel you can move it outboard (or inboard, in instances where the chainwheel is inboard of the spider) by a finite amount. Obviously you need to make sure your chainwheel bolts are long enough to accommodate the extra thickness and you may want to substitute a longer set if you make large adjustments. Not elegant by any means, but effective.

Silver ID 10mm, OD 14mm unless otherwise stated

Also great as axle spacers to adjust your hub width to fit your frame's dropout width. The stainless 1.9mm washers (20 mm outside diameter) are the best choice for re-spacing your axle.