I've always used 'shim stock', a packet of various steel shim stock in sizes running from .002 up to something like .035.
The pieces are about 4"x 6" each and ink stamped to ID the thickness.
Gives you a lot of matrl if you do a lot of different shop work.
Raiding an old feeler gauge for a piece of suitable thickness is the other way and you don't get stuck with a book of shim stock you'll never use.
I've always soft soldered the shim into place.
Tin the shim stock. Clean the hook well. I scrape them clean.
Flux both surfaces and clamp the shim in tight with a piece of round stock.
Get in there with some heat to flow the solder and add a touch when it flows. Tweak the clamp a touch tighter and let it cool.
No, the ribs won't fly off. But if you feel better clamping the upper rib to the short rib below,,do so.
File off the excess and polish up the lugs.
I know gluing things into place is the way lately, but for most things of this nature I just haven't wandered out into that brave new world yet.
