I notice that both 1/4" and 6mm are available for eccentric. Not sure why tho. is there a specific reason both sides are available. why not just have 6mm and add a shim?
Originally there were only 1/4" spacers. The 6mm spacers were later added to appease the metric purists. The 6mm spacers however don't leave room between the bottom of the plate and the extrusion for the heads of any bolts running back up through the plate and thus shims must be added whenever these bolts are necessary. But why spend an extra $0.25 for the additional shim at each wheel when the problem is easily eliminated by using the 1/4" spacers?
1/4 is 6.35mm - most of the world runs on metric but the are still country's on the imperial system, it doesn't bother me tbh as I can work in both its the old whitworth that throws me