It's easy to get confused in metric/imperial conversions. But why do you want such a short spacer?
Just to give a little more clearance for my left leg between the wheel and the central tunnel without bringing the wheel too close to me.
I found with the quick release there is a 2 stage lock (a bit like a bonnet catch). One time I accidentally drove the car with the wheel in the not fully latched position which gave about 0.5" more room and it made quite a difference to me.
