[AdamHeard]

We did this with the next size smaller pancake cylinder, which had an 8-32 Male thread and then used mcmaster 94165A423.

If you insist on keeping that cylinder size you can use mcmaster 90259A129 and retap the andymark block to 5/16-18.

If you also insist on using the female threaded cylinder, you can use a set screw/threaded rod (set screw is better due to the internal hex) to connect them.