This is the most common screw for Astoria/CMA equipment, but there is also a longer version available, so be sure you know which one you need prior to purchasing!
M5 x 12
This also fits all Brasilia and Gaggia equipment.
WARNING: This product can expose you to chemicals including lead, which are known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.