So what's interesting about a couple of rolls of solder? The roll on the left was bought some 40-50 years ago, when I was a kid playing around with electronics. The diameter suited valve (tube) circuits assembled underneath an aluminium chassis using axial components, solder tags, and wires, not even PCBs. It went into storage while life happened: getting an education, then a job and a home. A few years back I started owning all my time again so I put it to use. Soon it will be gone. End of an era. No I won't write a song about how good the old solder was. 🤪

On the right is what I'm using these days. The smaller diameter suits current designs better because it's slimmer and there is a greater proportion of flux to solder. Furthermore it's 63/37 Sn/Pb. (Look up eutectic.)