L-Acoustics WST K2 Rigging Manual page 39

Turn the bars to release the spring-loaded safety and slide them out.
Insert the spring-loaded safety in the LA-RAK rails, give a quarter turn and slide the bar until the safety locks into place.
Insert the coupling bars:
 from the back for a negative angle (rear extension),
 from the front for a positive angle (front extension).
Always insert so the metallic safety is pointed upward (depending on the tilt angle).
K2_RM_EN_0.5
5. Attach the LA-RAK on the K2-BUMP.
Remove the LA-RAK coupling bars
Position the LA-RAK on the rails.
Secure the LA-RAK with the coupling bars.
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