: If you just want to merge them into one large .7z file without extracting yet, you can use the Command Prompt (Windows): copy /b Tc-Yose-011.7z.001 + Tc-Yose-011.7z.002 Tc-Yose-011.7z

You do not need to manually join them; extraction software does this automatically:

: If the extraction fails with an "Unexpected end of data" error, you are likely missing one of the numbered volumes.