The files are in the format:
php_pthreads-X.XX-Y.Y-ts-vcZZ-x86.zip
where
X.XX is the version of the phpthreads-win32
Y.Y is the base version of PHP that you are running
ZZ is ?? (version of compiler?)
Currently, 0.44 is the latest release of phpthreads-win32, so X.XX = 0.44
If you are running PHP 5.3.13, then Y.Y = 5.3
If you are running PHP 5.5.0, then Y.Y=5.5
etc
php_pthreads-0.44-5.3-ts-vc9-x86.zip
php_pthreads-0.44-5.4-ts-vc9-x86.zip
php_pthreads-0.44-5.5-ts-vc11-x64.zip
php_pthreads-0.44-5.5-ts-vc11-x86.zip