Attachment answers / Thumbs & grapples
What is the difference between a mechanical and a hydraulic thumb?
Short answer
A mechanical thumb is set by hand into one of several fixed positions and needs no hydraulics. A hydraulic thumb is driven by a cylinder from the cab and adjusts continuously. Mechanical is cheaper and simpler; hydraulic is faster and grips far more material.
Last reviewed August 2026 · Quarrymark Attachments sales engineering desk
A thumb turns an excavator bucket into a set of pliers. Which type you buy comes down to how often you will change its position during a shift.
The mechanical thumb
A mechanical thumb pins to the stick and locks into one of typically three to five stored positions, set by hand. To change position the operator gets out, pulls a pin, moves the thumb and re-pins it. Some designs let the operator move it with the bucket, which saves the wrestling but not the dismount.
There are no hoses, no cylinder, no auxiliary circuit and nothing to leak. The purchase price is roughly half that of a hydraulic thumb of the same class, and installation is a bracket and two pins rather than plumbing down the stick. For a machine that handles broadly similar material all day - pipe, rock of one size, brush - it is a genuinely good answer.
The hydraulic thumb
A hydraulic thumb has its own cylinder and is adjusted continuously from the cab. It can hold a 4 in. root ball and then a 30 in. pipe without the operator leaving the seat, it can apply real clamping pressure rather than relying on bucket curl to trap the object, and it can hold something while the machine repositions.
It costs more, it needs an auxiliary circuit, and it needs the hoses run and protected. The clamping force also means it can be over-used: a hydraulic thumb will hold onto something hard enough to bend the thumb if the operator uses the machine's swing to lever with it.
Progressive link, and why it matters more than the type
Both types come in fixed-position and progressive-link designs. A progressive link keeps the thumb's tip roughly parallel to the bucket teeth through the full curl arc, so the thumb and bucket meet cleanly across the whole range instead of only in one sweet spot. It is the difference between a thumb that grips a small object and one that only really works on large ones.
If you are choosing between a progressive-link mechanical thumb and a fixed hydraulic one at the same price, the progressive link is usually the better tool.
Sizing
Thumbs are specified by weight class and by their tine dimensions - our range runs a 20 x 39 in. thumb for 6-10 t machines, a 26 x 45 in. for 9-16 t, a 30 x 54 in. for 16-25 t and a 45 x 75 in. for 30-50 t machines. The width should suit the bucket you use most; a thumb much narrower than the bucket will only grip in the centre, and a thumb wider than the bucket will foul the side plates.
Whichever you choose, the thumb must be mounted to a stick that can take it. A bolt-on or weld-on mounting bracket concentrates load into the stick, and a thumb fitted to a stick without adequate reinforcement is a documented way to crack one.
Can I add a hydraulic thumb to a machine with no auxiliary circuit?
Yes, but it means adding a circuit: a valve section or a diverter, a line down the boom and stick, and a control. Factor that installation cost in when you compare against a mechanical thumb.
Will a thumb work with a quick coupler?
It can, but the coupler pushes the bucket further out and changes where the bucket teeth meet the thumb. Thumbs used with couplers should be specified with the coupler in the loop, not added afterwards.
Does a thumb reduce my machine's lift capacity?
Yes - its weight sits at the end of the stick, exactly where lift capacity is lowest. It is a permanent reduction whether the thumb is stowed or working.
