Got some new Sun Ringle wheels and a new wide bottomed cog from Superstar. All looking great. But when I put the cog on the freewheel there is some back and forth play. This is because the splines on the freehub are all narrow as are the ones on the cog, so they don’t fill the space between the splines on the freehub, that make sense? Once the lockring is tightend there is no play but I’ve not tried riding it yet. Should be alright though eh? Don’t want to damage my nice new wheels though.

since the freewheel stops any force rotating the sprocket to the back of the splines it will stay tight against the front of the splines so nothing really to worry about.

That’s what I was thinking but never encountered this before. Probably wouldn’t have this issue with any other combination of hubs or cogs or cassettes that I’ve got.

Maybe both manufacturers have erred on the side of caution by allowing great clearance so that should a sprocket bite into the aluminium body and displace some material into the spline space then there’s still room to be able to disengage the sprockets and pull them off the freehub body?