This Kit includes four Magnets for the Post Mount
 
These 20 mm diameter magents are replacements for the original Post Mount Magnets.  These neodymium magnets are very strong  and provide a rock solid connection.  The kit includes four magents that easily thread into your Post Mount.  The magnets are threaded M5 and fit perfectly in the Post Mount.  
 
When we install these magnets in the shop we use a drop of loctite and torque them with pliers until snug.  You can install them in finger tight if you keep an eye on them and tighten as required.