If you have ever bought an attachment that should have fit your 2x72 and it showed up 1-16 in too small (or too big), you already know the truth: “tooling arm size” is not a vibe. It is a hard measurement that decides whether your grinder feels like a precision machine or a rattly science project.
This is a practical guide to 2x72 grinder tooling arm sizes - what the common standards actually are, where people get tripped up, and how to choose lengths that stay rigid under load. The goal is simple: your arms slide in clean, lock down square, and run every platen, contact wheel, small-wheel, and work rest you throw at them.
What “tooling arm size” means on a 2x72
On most modern 2x72 platforms, the tooling arm is the square tube (or solid bar) that slides into the grinder’s receiver tube. Attachments mount to the arm, the arm locks with a bolt or cam, and the whole assembly becomes the backbone for tracking stability and repeatable setup.
When makers say “2x72 grinder tooling arm sizes,” they are usually talking about the cross section of that arm: 1 inch, 1-1/4 inch, 1-1/2 inch, or 2 inch square. That number is the outside dimension of the square tube, not the inside and not some nominal “close enough” dimension.
The second part of tooling arm sizing is length. Length decides leverage. The farther an attachment sits from the receiver, the more it wants to deflect under pressure. For aggressive stock removal, length and rigidity matter just as much as horsepower.
The common standards: 1.5 inch dominates, but it’s not universal
If you are building around the current ecosystem of attachments, 1.5 inch square tooling arms are the closest thing to a default. Plenty of serious grinders are designed around 1.5 inch arms because they strike the best balance: big enough to be stiff, small enough to keep receivers compact and accessory costs reasonable.
That said, you will still run into 1-1/4 inch arms on lighter machines and older designs, and 2 inch arms on heavier industrial builds or custom rigs where maximum stiffness is the priority. A few compact grinders use 1 inch systems for tight packaging.
Here is the hard part: even if two brands both claim “1.5 inch tooling arm,” the real-world fit can vary because of wall thickness, weld distortion, powder coat, burrs, and how tightly the receiver was built. The standard is the number, but your grinder’s receiver is the judge.
Fit is about clearance, not force
A good tooling arm fit slides in with hand pressure, doesn’t rock side-to-side, and locks without needing to crank the bolt like you’re tightening lug nuts. If you have to hammer it in, you are going to hate swapping setups. If it wiggles, you will chase belt tracking and inconsistent angles.
Expect that some arms may need a light deburr on the corners, and some receivers may need paint cleaned out. That is normal shop work. What you do not want is “mystery clearance” where the arm is obviously undersized and the clamp just bends things into place.
How to measure your tooling arm size the right way
Don’t measure the receiver opening and guess. Measure an arm that fits, or measure the receiver’s internal dimension and compare carefully.
Use calipers if you have them. You are looking for the outside dimension of the tooling arm tube. A true 1.5 inch arm should read close to 1.500 inches on the flat. If you are seeing 1.480 or 1.470, you may have a nominal tube that is undersized, or you are on a smaller standard.
Also measure corner-to-corner (diagonal) if you suspect the tube is out of square. A bent or twisted tube can “fit” but bind in spots, and it will never feel consistent when you adjust in and out.
Finally, measure your receiver depth. That number matters when you pick arm length, because the portion inside the receiver is what gives you support.
Length: the most overlooked part of 2x72 grinder tooling arm sizes
Cross section gets the attention, but length is what decides how your grinder behaves under pressure.
A short arm keeps attachments close to the chassis. That reduces leverage and deflection. If you do heavy platen work, hog bevels, or run a small-wheel attachment with real pressure, shorter is usually better.
A longer arm gives you reach. That matters when you want more working room, clearance for big contact wheels, or space for specialty attachments that need extra standoff.
The trade-off is simple: every inch you move the load outward increases flex. Flex shows up as chatter, inconsistent plunge lines, and “why is my belt wandering when I lean in?” moments.
A practical way to choose arm length
Think in terms of engagement. You want a solid portion of the tooling arm buried inside the receiver at all times - especially at your most extended working position. If your receiver is, say, 6 inches deep and you routinely run the arm almost pulled out, you have effectively turned your arm into a long lever with a short fulcrum.
For most shops, it is smarter to have multiple arms in different lengths than to run one extra-long arm for everything. Swapping a tooling arm takes seconds. Fighting flex takes the rest of the day.
Wall thickness and material: “size” includes stiffness
Two 1.5 inch tooling arms can behave totally differently depending on wall thickness and steel quality. Thin-wall tube is lighter and cheaper, but it will twist more under load. Thicker-wall tube is stiffer and holds alignment better when you clamp hard or slam the platen into a hot billet.
If you do knife bevels where repeatability matters, stiffness is not a luxury. It is what keeps your work rest and platen staying square to the belt after you lock in your angle.
Also pay attention to the receiver design. A good receiver supports the arm along a meaningful length and clamps it without point-loading one corner. When the clamp presses evenly, the arm stays square instead of cocking.
Attachment compatibility: why “standard” still bites people
Most attachment makers build around a few common assumptions: a specific arm size (often 1.5 inch), a certain receiver height from the platen, and a predictable tracking geometry.
When you mix platforms, the arm size is only the first hurdle. The next is where the attachment ends up in space. A small-wheel attachment that technically fits your arm might put the wheels too high or too low relative to your drive wheel and tracking wheel. You can shim and hack, but you are burning time.
If you are planning a modular ecosystem, pick a tooling arm size that has broad support and stick with it across your grinder’s stations. That includes your work rest arms, your platen arms, and any auxiliary arms for specialty setups.
Multiple receivers and dedicated arms: the shop-speed upgrade
Once you start using your grinder like a production tool, the real win is not just “what arm size fits.” It is how fast you can change operations without losing settings.
Dedicated arms let you keep a platen aligned, keep a work rest height consistent, and keep a small-wheel attachment ready to go. Instead of loosening bolts, sliding, measuring, and re-squaring, you swap an arm and get back to grinding.
This is where a consistent arm size pays off. One standard size across your machine means your spares are actually spares. It also means every new accessory you add has a clean place to live.
If you are building a grinder system that is meant to scale, brands with an integrated accessory ecosystem make that easier. Diktator Grinders builds its platforms and add-ons around a modular approach that’s meant to stay tight and repeatable as you expand - you can see the ecosystem at https://diktatorgrinder.com.
Troubleshooting bad fit without guessing
If an arm does not slide smoothly, don’t automatically assume the arm is wrong. Check the simple stuff first.
Paint and powder coat inside the receiver can create high spots, especially near weld seams. Burrs on the arm corners can scrape and bind. If the receiver tube was welded and pulled slightly out of square, it can grab in one orientation and feel loose in another.
If an arm is loose, confirm you are not mixing 1.5 inch and 1-1/4 inch parts. That happens more often than people admit, especially when buying used attachments. Also check whether the clamp is actually clamping the flat of the arm. A clamp that hits near an edge can feel “tight” while still allowing rock.
When you do need to correct fit, remove as little material as possible and do it evenly. You want a controlled, repeatable slip fit, not a wobbly arm that “works if you crank it.”
Choosing your standard: what to run if you’re buying today
If you are setting up a grinder from scratch and you want the widest practical compatibility for modern knife making and fab work, 1.5 inch square tooling arms are the safest bet. They are stiff enough for real grinding pressure and common enough that you can source multiple arms and attachments without getting boxed in.
If your grinder is compact and you value light weight and minimal footprint, smaller arms can make sense - but understand the trade-off. You may need to baby the pressure or accept more deflection on long extensions.
If you are building a heavy, high-horsepower machine meant to lean on big contact wheels and aggressive ceramic belts all day, 2 inch arms can be the right call. You are buying stiffness and stability, and you will feel it. You are also committing to a less universal accessory pool.
The honest answer is “it depends,” but it depends on how hard you grind and how much you value cross-compatibility. Decide which problem you would rather not have: a slightly bulkier system that stays rigid, or a smaller system that may need more finesse.
If you want one simple rule that holds up in real shops, it is this: pick the tooling arm size that your preferred attachments are built around, then buy extra arms in smart lengths so you are not forcing one setup to do everything.
Your grinder should feel like it wants to work with you. When the tooling arms fit right, lock down square, and don’t flex when you lean in, you stop thinking about hardware and start thinking about grind lines. That is where the fun - and the production speed - actually lives.
