OK bosses are the nuts embedded in a frame that you can screw accessories in like racks and bottle cages. They can be either welded in or held in compression using Rivnuts, which are expanding nuts that can be locked into a hole. Now the good news is you’ll probably never need to know this because they rarely break, the bad news is I had to become familiar with them because one of mine broke.
The first time I screwed a water bottle cage into my frame 3 years ago I thought something wasn’t quite right, even though the bolt was tight it didn’t feel that tight, but it seemed to be fine so I left it alone. Over the years this cage would rattle forcing me to tighten the bolt every few months. Eventually it just started spinning when I tried to tighten it.
The bolt became stuck in the boss and the only way I could think to get it out was with a hacksaw, not very elegant but effective. Now the boss and half the bolt are banging around in my down tube. They may fall out next time I take the crank out.
Replacing the boss was a challenge I didn’t expect. I took it t my go to bike shop, Carbondale Cycle, and Choak didn’t have the parts to fix it, I tried Phoenix Cycles and they couldnt’ find them either. I stopped by Bike World in Paducah KY without my bike just to see, and they had the Rivnuts but would only install them, they wouldnt’ sell me one to take home. They told me it was too complicated for the “home mechanic” to do and I didn’t have the tools required.
The fine folks at Bike World didn’t know it but they had just slapped me in the face with an iron gauntlet. First off, nothing is to complicated for the dedicated “home mechanic” and if everyone waited for the proper tool to come along we’d still be living in mud huts.
A 5 minute google search revealed the Park tool website’s explanation for installing rivnuts using a hub. I found some on ebay for 5 dollars. It took me about 5 minutes to install the nut, hmm, lots of 5s. Lets roll the footage.