K1 1.5GT Belt Retainer.

Recommended printing options

Material: ABS/ABS-CF

Nozzle diameter: 0.4mm

Layer height: 0.1mm

Wall loops: at least 4

Inner/Outer wall/Supports thickness: 0,6mm/0.4mm/0.35mm

Top/bottom shells: at least 5

Infill: 100%

Supports: Tree,  with “Remove small overhangs” option turned on.

The best printing orientation: 

BOM

Printed belt retainers: 2x (will be the better to print more then 2x to keep spare)

1.5GT 26T pulley: 2x

1.5GT open ended timing belt of needed length: 2x.

printer.cfg

[stepper_x]
...
# rotation_distance: 40
rotation_distance: 39
...
[stepper_y]
...
# rotation_distance: 40
rotation_distance: 39
...

Also I had to tune TMC2209 virtual endstop sensitivity. May be you also need to tune it:

[tmc2209 stepper_x]
...
# driver_SGTHRS: 75
driver_SGTHRS: 82
...
[tmc2209 stepper_y]
...
# driver_SGTHRS: 75
driver_SGTHRS: 82
...

I use such retainers for a month on my K1SE together with pair of D3VIL DesignKraken v2 NEMA17 motors on X and Y axes and X-axis rail mod and achieved noticeable VFA reduction .

I use POWGE 1.5GT Pulleys and belts:

However, I still testing that.