Originally Posted by
tFUnK
Has anyone else done something similar? I already understand this is not ideal, but is this a truly terrible idea?
It's a bad idea.
First position cogs have a builtin spacer so they have good spline engagement overhanging the end of the freehub, and serrations to prevent lock ring rotation. While you can probably get away with no serrations, poor engagement with the freehub splines is a bad idea especially if they're aluminum like Campagnolo spline freehub bodies and many aftermarket Shimano/SRAM pattern parts.
Just buy a cassette with a 13T first position cog. The lock rings are the same for all 12T+ first position cogs.
13-14-15-16-17-18-19-21-23-26 is my favorite for the 10 speed era.
Having issues acquiring 13-21 8 cog cassettes after Campagnolo moved on to 9, I probably have enough 10 cog 13-26 spares for 75,000 miles in my parts bin,