This is was a father-son project to develop this. We learned after taking apart 5 steering columns that we had 5 broken horn button retainers. So we developed one with the same geometry; but much stronger and also serviceable. This fits the K/KB series trucks as well as the L, R, and S series trucks. This is a combination of laser-cut stainless with 3D printed plastic. 
https://www.youtube.com/watch?v=Hl09kqRoBB8
 
$9 shipping