When S&S sends you a set of couplers, they also send some little stainless discs that you can braze into the inside to seal off the rest of the tube from the coupler. I usually throw them away (I like to leave the tube open so I can get framesaver into it, plus the discs are like 20+ gauge or something and just burn to a crisp when you’re brazing them unless you’re a HUGE stud with the torch/56% – which I’m not) but sometimes I would just toss them into the bin where I keep flux and flux brushes and other “dirty” crap that I don’t want touching other stuff.
Wow, that is a lot of random little stainless discs. I think I do 3 or 4 coupled bikes a year, and over 8 years, that’s a decent number of bikes, and quite a collection of useless super thin stainless steel circles. The nasty flux goo is quite gross. I need to be less of a slob!