If you've got an uber-cool Rickenbacker 336/12, 366/12, or 456/12 guitar, you may find that it's been partially dismantled over the years.  One of the first parts to disappear is the unique arm retaining screw.
Not to worry, boys and girls; we've got you covered.  
 
Made of chrome-plated steel, this is a dead-nuts match for the original: same length, same thread, same knurled top.
 
Jump on it.