Window guide

Thanks for your post! The black nylon piece shown here reminds me of the 39-529 Truth Hardware Track Slider; it is compatible with the 39-528 Casement Track. 

These parts are used with the 39-253LB and 39-253RB Encore Dual Arm Operator. To determine if this is the correct replacement match, carefully look over the specifications and compare them. They can be found on the website.

The compatible cover and handle kits can be found tagged below.

Alternate image for 39-529

Alternate view with measurements