You need 10 1/8" spokes to lace a kickback to a drop center rim. 14 ga. spokes were standard. Everything is metric now. :lol: Gary
edited to add: 10 1/8" if you are using the old style long nipples. If you are using the medium or short nipples you'll probably need 10 1/4" spokes.
You can remember the kickback spoke length as it will be 1/2" shorter than the spokes on the same rim with a Bendix or ND single speed hub.
S-7 is 10 7/8" with standard hub, 10 3/8" with kickback.
S2 or drop center is 10 5/8" standard, 10 1/8" with kickback.
Again, you may have to add or subtract 1/8" depending on the nipples you use or if your rims are slightly off standard. Gary