ruby-thread | Various extensions to the base thread library | Architecture library

There are several issues:

• You'd not spawn thousands of threads, use a connection pool (e.g https://github.com/mperham/connection_pool) so you have maximum 20-30 concurrent requests going (this maximum number should be determined by testing at which point network performance drops and you get these timeouts).
• It's difficult to guarantee that your code is not broken when you use threads, that's why I suggest you use something where others figured it out for you, like https://github.com/httprb/http (with examples for thread safety and concurrent requests like https://github.com/httprb/http/wiki/Thread-Safety). There are other libs out there (Typhoeus, patron) but this one is pure Ruby so basic thread safety is easier to achieve.
• You should not use Timeout (see https://jvns.ca/blog/2015/11/27/why-rubys-timeout-is-dangerous-and-thread-dot-raise-is-terrifying and https://medium.com/@adamhooper/in-ruby-dont-use-timeout-77d9d4e5a001). Use IO.select or something else.

Also, I suggest you learn about threading issues like deadlocks, starvations and all the gotchas. In your case you are doing a starvation of network resources because all the threads are fighting for bandwidth/network.