There should be a few mm each side so the the gap between the drums is so minimal that it prevents the drums tilting on the shaft and bushes. This evens out the load on the axle shaft and prevents it flexing. Not so tight that it wears the adjusting thrust surfaces, which is what the grease nipples lubricate, not the bearings. I squirt oil at least daily anywhere and everywhere I think it would be beneficial.So thats just an over thought spacer. How much play should there be, between the drums and the shaft as this looks like a lot?