Attachment answers / Sizing & fitment
What does the tonnage class on an attachment mean?
Short answer
The tonnage class is the machine operating-weight window an attachment was engineered for - plate thickness, side-plate height, pin-boss size and wear package. A bucket marked 10-15 t is built for the breakout force a 10-15 t excavator produces. Outside it, something is overloaded.
Last reviewed August 2026 · Quarrymark Attachments sales engineering desk
Attachment listings quote a range like 4-6.5 t or 16-25 t. That is the operating weight of the carrier, in metric tonnes, that the attachment was designed around. It is not a suggestion and it is not a size label - it is the load case the steel was drawn to.
What actually changes between classes
Moving up a class changes four things at once. Plate thickness on the wear surfaces goes up. Side-plate height and the wrapper radius go up, so the bucket holds material a stronger machine can carry. Pin bosses get larger bores and thicker doublers to take a bigger pin. And the tooth or adapter system moves to a heavier series, because a bigger machine can drive a bigger tooth into harder material.
That is why a 24 in. bucket for a 2-3 t mini and a 24 in. bucket for a 16-25 t excavator are not the same product at a different price. In our own catalog they are a 24 in. digging bucket at 35 mm pins and a 24 in. heavy-duty digging bucket at 80 mm pins - the same width, roughly double the price, and completely different steel.
The two failure modes
Under-classed attachment on a big machine: the machine wins. Side plates fold, the wrapper cracks at the heel, the pin bosses egg out and the bucket develops play that accelerates the wear. This is the common one, because the attachment fits and digs beautifully for a few weeks.
Over-classed attachment on a small machine: the attachment wins. The machine cannot fill it at reach, cycle times go up, and every load pushes the tipping load - which on a mini excavator is a real stability problem, not an abstract one. You also lose the breakout force to the extra empty weight before you have moved any dirt.
Why the class also tells you the pin size
Manufacturers scale the linkage with the machine, so weight class and pin diameter track each other closely. Across the machines in our database, 1-2 t machines run 25-30 mm pins, 2-4 t run 35-40 mm, 4-6.5 t run 45 mm, 7-10 t run 50 mm, 10-16 t run 60-65 mm, 16-25 t run 80 mm, and 25 t and up run 90-100 mm. The class is therefore a useful first filter even before you measure anything.
It is a filter, not a guarantee. Manufacturers do vary within a class, and some models are offered with more than one stick option. Confirm the pin diameter and the stick width on the machine itself before you order.
My machine sits between two tonnage bands. Which do I pick?
Pick the band that contains your operating weight. If you are genuinely on the boundary, go to the heavier band when you dig rock, shot rock or recycled concrete, and to the lighter band when you dig dirt and want cycle time.
Is tonnage class the same as bucket capacity?
No. Tonnage class describes the carrier the attachment suits. Capacity, quoted in cubic yards struck or heaped, describes how much the bucket holds. Two buckets in the same class can differ substantially in capacity depending on width and profile.
