The Rexstix Locking Rod Butt and Rexfly Chest Harness allows you to customize a split grip rod. Adapter is glass-filled nylon with an aluminum latch and stainless steel spring.

Assembly video https://youtu.be/Ppt7lofShcE

Casting rods may be up or down-locking reel seat depending on rod and how far away you want the adapter from the reel.. Spinning rods should have a down-locking reel seat for one arm fishing.