Join Date: Jul 2005
Location: Backwoods of Ontario
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Googling Thun bottom bracket brings up results for 6 notch BB tools like the low end Campy square tapers, which jives with the description of being a cartridge BB.
Makes me wonder whether you crankset uses a ISO taper, however, googling the crankset brings up some other bike specs that seem to use this crankset with Tiagra and Sora components which would be JIS taper.
Either way, you should be able to replace it with a Shimano unit and keep your crankset, but I'm too lazy to chase any further BB specs at this time.
The Thun cartridge should come out with a Park BBT4 tool or equivalent.