I assume your FEL as a skid steer quick attach adapter on the ends of the arms. Here's the QA on my Mahindra 5525
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I couldn't afford a store-bought accumulator-grapple, so I made my own. It's an 8-bale squeeze (2-twine small bales) with a detachable accumulator that
rides on the arms of the bale squeeze.
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You can get an idea of the design of the accumulator from these photos.
The bale squeeze has a skid steer QA plate welded to its backside
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The accumulator was pretty easy to build from rough sketches.