Pinning happens on the day of expiration which is a 700 profit club Friday. It can also start happening as early as Thursday the day just prior to its expiration date. Activity usually picks up on both dates. The things to look for to determine where the pinning will happen is the volume and open interest of the various option contracts. The contracts with the most volume and open interest on the call and put side should be looked at. The reason for this is because the writers of the contracts want them to expire worthless so that they keep the premium. The strike price that is in between the call and put is usually the price of the pin. Weekly pinning is now occurring since the arrival of weekly contracts such as AAPL.
Because of the Delta hedgers and market manipulators, the stock volatility drops. The price of the stock will tend to cluster around the inside call and put benefactors. The stock will tend to cluster towards the strike price with the most amount of beneficial interest of the writers. You can easily determine this by adding up the open interest of both the call and the puts. The strike price between the calls and puts will more than likely be the area of the pin. Pinning in stocks is very common. It happens because of hedgers and manipulators. The day of the pinning is on Fridays. The characteristics usually have the most activity in the call and puts. The next time you pull up a quote on Apple on a Friday try to see if you can figure out where the pinning price will be.