One of the frequent pieces of equipment used on kayaks with forward mounted flush rod holders is the Scotty Gimbal Mount. As you can see in the photo, the Gimbal Mount is being used on a Malibu Kayaks eXtreme model and is placed in the forward flush mount rod holder. The flush mount rod holder has a bar running across the bottom of the mount that the indentation of the Gimbal Mount rests on.
Malibu Kayaks Extreme fishing kayak

Essentially, utilizing the mount enables you to use a flush mounted rod holder to adapt a Scotty Rod Holder of some type to it. When you use the Scotty's you can adjust the upward-downward rod angle and rotate the rod holder head so you can sweep it forward or backwards.

It makes for a nice adjustable unit. In the photo, the Gimbal Mount has a Scotty Powerlock rod holder plugged into it. The Powerlock is one of the more popular rod holders being used in conjunction with the Gimbal Mount being used today. Both are made from engineering nylon for years of trouble free service which is very important when used in or around saltwater.