Jth 3185-

Hello,

Thanks for reaching out! The attachment at the end of your long arm appears to be the 39-529 Truth Hardware Track Slider. This is used with the 39-253RB Encore Dual Arm Operator. The opposite version is the 39-253LB.

I'm confident this should be what you need but be sure to take a look over the specifications and compare them.

The other compatible hardware and accessories can be found tagged below this thread.

Dimensions for 39-253RB