What is a numeric extension?

I found files from old pc. It's extension is 001, 002, 003...etc.

How can I see these files? What is these?

Thank you, any comments.

What is a numeric extension?regal theater

those are part of a rar archive. open them using WinRar program.

What is a numeric extension?performing art center opera theater

Those look like old .rar archives. But unless you know exactly what they are, they are probably just database files from a specific program.