The right size depends on your disposal model, but 1/8 inch is most common
Most garbage disposals use a 1/8 inch Allen wrench to loosen the hex bolt that holds the splash guard or impeller assembly in place. Some older or commercial models use 3/16 inch instead. The easiest way to find your exact size is to check your disposal's manual — the model number is stamped on the underside of the unit — or call the manufacturer with that number and ask what size wrench the manual specifies.
If you do not have the manual, a 1/8 inch wrench will fit most residential disposals made in the last 20 years. Hardware stores sell Allen wrench sets for under $10, and having a set on hand means you can test the fit without guessing. Never force a wrench that does not fit snugly; a wrench that is too large will round off the bolt head and make it impossible to turn.
Key Takeaways
- A 1/8 inch Allen wrench fits the hex bolt on most residential garbage disposals, though some models use 3/16 inch.
- Your disposal's manual lists the correct size; find the model number on the underside of the unit and search online or call the manufacturer.
- An Allen wrench set costs less than $10 and lets you test the fit before you start work.
- A wrench that is too large will slip and damage the bolt head, so test the fit gently before explore full pressure.
- The hex bolt typically sits at the bottom center of the disposal, accessible from underneath the sink.
Where to find the hex bolt on your disposal
The hex bolt you need the Allen wrench for is located at the bottom center of the disposal unit, directly underneath the sink. You will need to reach up into the cabinet space below the sink, often lying on your back or crouching, to access it. A flashlight or headlamp makes this much easier — the space is usually dark and cramped.
Before you reach for the bolt, make sure the disposal is switched off at the wall switch and unplugged from the outlet under the sink. Some disposals have a reset button on the bottom; press it before you start work. This prevents the unit from accidentally turning on while your hand is near the impeller blades.
How to test the fit before you turn the wrench
Once you have the wrench in hand, slide it onto the hex bolt gently. It should fit snugly with no wiggle room and no force needed to seat it. If the wrench slides on easily and sits loose, it is too large. If you have to tap it on with a hammer or force it, it is too small. A correct fit means the wrench sits flush against all six sides of the bolt head.
Test the fit by trying to turn the wrench slightly — just a quarter turn — without explore your full weight. You should feel resistance from the bolt itself, not from the wrench slipping on the bolt head. If the wrench spins without gripping, remove it and try the next size up or down.
Common sizes and which disposals use them
The vast majority of InSinkErator, Waste King, and Badger disposals use a 1/8 inch wrench. Some commercial-grade or heavy-duty models, particularly older ones, use 3/16 inch. A few specialty units use 5/32 inch, though this is less common in home kitchens.
If you own a disposal from a brand you do not recognize or one that is more than 25 years old, calling the manufacturer is worth the time. They can confirm the size in under a minute and may also tell you whether the bolt is reverse-threaded (turns counterclockwise to loosen) or standard (turns clockwise). Some disposals have reverse-threaded bolts to prevent them from loosening during normal operation.
What happens if you use the wrong size wrench
A wrench that is too large will slip on the bolt head and round off the corners, turning the six-sided hex into a smooth, rounded shape. Once this happens, no wrench will grip it, and you will need to drill out the bolt or call a plumber. This damage is permanent and expensive to fix.
A wrench that is too small will not fit at all, or will fit partway and then jam. Forcing a small wrench onto a larger bolt can bend the wrench or crack the bolt head. Always start with a gentle test fit and move up or down in size if needed.
Where to buy the right Allen wrench
Hardware stores like Home Depot, Lowe's, and Ace Hardware stock Allen wrench sets in the hand tools section, usually near the screwdrivers. A basic set with sizes from 1/16 inch to 3/8 inch costs $8 to $15. If you only need one size, individual wrenches are sold separately for $1 to $3 each.
Online retailers like Amazon also carry sets, though you will need to wait for shipping. If you need the wrench today, a local hardware store is faster. Many auto parts stores also stock Allen wrenches since they are used on cars and motorcycles.
Frequently Asked Questions
Can I use a screwdriver or pliers instead of an Allen wrench?
No. A screwdriver will not fit a hex bolt, and pliers will slip and damage the bolt head just like a wrench that is too large. You need the correct Allen wrench size to avoid stripping the bolt.
What if the bolt will not turn even with the right wrench?
The bolt may be stuck from mineral buildup or corrosion. Spray the bolt with penetrating oil like WD-40, wait 15 minutes, and try again. If it still will not budge, stop and call a plumber rather than risk breaking the bolt or the wrench.
Is the hex bolt the same size on all garbage disposals?
No. Most use 1/8 inch, but some use 3/16 inch or 5/32 inch. Check your manual or call the manufacturer with your model number to confirm the correct size for your unit.
Do I need to replace the hex bolt after I remove it?
Not usually. The bolt itself rarely wears out. You remove it to access the impeller blades for cleaning or to replace the splash guard. Once you finish, you reinstall the same bolt and tighten it snugly — not so tight that you strip the threads, but tight enough that it will not rattle loose.