Suitable for all our size poles, as well as for mega umbrellas, and often referred to just as Enhanced Bases..  The bases are available for 1.5″, 2″ inch, 3 inch and 4 inch poles.  Comprises two parts:  a flush mount base (which is permanently installed in the boat), and a vertical enhanced socket that threads in with a Higbee thread (the same thread used on race car wheels) – when the socket is removed, a stainless steel plug is threaded in to provide a beautiful finished appearance.  Patent pending.  For the 3-inch and 4-inch Enhanced Vertical Mounting bases, a backing plate is included.  We recommend attaching the pole to the socket permanently, and to do this, it is important to DRILL the hole and tap it and use MACHINE SCREWS ONLY – do NOT use self tapping screws.  If you have any questions about this process, please call or email us, we are at your service any time you need assistance or guidance with our products.