For 12T
It gives the chain more clearance so that the chain won't touch the lockring.
Other recommended products
GIGAS
Sales price : JPY 9,200 - 22,560
GIGAS Sprocket, ultra light, perfectly round, low friction and very smooth, made of GIGAS aluminum alloy
Tread : BC1.29x24T L
Material : Cr-Mo steel
Size : 2 sizes, For 12T / For 13T and larger sprockets