Caterpillar® Center-Lock Pin-Grabber Coupler

Updated Sep 30, 2010

The new Caterpillar Center-Lock Pin-Grabber coupler for Cat® hydraulic excavator models 311 through 385 uses a patented over-center locking mechanism and two hydraulic locking features to assure positive work-tool attachment. The new over-center locking technology promotes jobsite safety and allows operators to quickly, simply and confidently engage and disengage work tools regardless of boom and stick position. The Center-Lock coupler accommodates the same range of Cat work tools as previous pin-grabber couplers, as well as a broad range of other brands of buckets and tools. 


When the operator uses an in-cab switch to engage the Center-Lock coupler with a work tool, the coupler’s robust cylinder extends to close the primary hook around the tool’s rear pin. As the cylinder rod continues to close around the rear pin, the cylinder housing adjusts its position and forces a combination of three attached parts- center-lock rocker, connector link and secondary lock- to snap into an over-center position (much like closing the handles of locking pliers). This action forces the secondary lock to grip the forward pin. 


Once the coupler locks, the mechanical principles involved in its over-center locking technology assure that any working forces applied to the pins will serve only to increase the coupler’s grip. Constant hydraulic force exerted by the cylinder and the action of a counterbalance valve provide additional locking forces, supplementing that of the mechanical lock. 


The Center-Lock coupler remains positively closed until the operator takes the deliberate actions of activating the in-cab switch and extending the bucket cylinder. For the operator’s convenience and for jobsite safety, the secondary lock is distinctly visible from the cab and provides an unmistakable indicator of the coupler’s status- whether locked or unlocked. 


Because the new Center-Lock coupler eliminates the blocking bar and spring pack required with conventional pin-grabber designs, the operator no longer needs to completely curl the boom and stick (thus inverting the coupler) when engaging a work tool. The Center-Lock design requires only that the bucket cylinder be extended to activate locking and unlocking functions, and this action is independent of boom and stick position. The resulting advantage is that the operator can engage and disengage tools with the boom and stick at full extension, a valuable feature when changing tools in low-overhead situations, such as near power lines. 


Maintaining the new Center-Lock coupler requires only daily greasing, and to promote trouble-free operation, a new jumper-line routing helps avoid pinching or snagging on jobsite hazards. 


For more information about the Center-Lock Pin Grabber coupler, customers should contact their local Caterpillar dealer or go to

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