Hi all hope everyone staying safe
Just thought I would add what I do to repair a bulging split mainspring barrel, I drill out the old spring hook, then dress the barrel back to shape plug hole then silver solder, then I drill fresh hole 180 deg round, I then turn a new hook on the lathe
( some people use a nail ) but would rather turn a hook as I can put a step in it to rest inside the barrel, that way I know that it will stay in place after dressing the hook into the slight countersink, file and polish ( the reason I use silver solder it’s same colour as the brass ) as I repair torsion clocks and the barrel can be seen through the glass dome.
Dell