Are Circular Saw Blade Bolts Reverse Threaded? Depends on the Side

Yes — on many circular saws, the arbor bolt is reverse-threaded (left-hand thread) specifically on the side where the blade would otherwise loosen itself during normal cutting. Which side that is depends on which way the saw’s motor spins the blade, not on the brand or price of the saw.

This trips up a lot of people the first time they change a blade, because the instinct is always “righty-tighty, lefty-loosey.” On the reverse-threaded side, that instinct is backwards, and forcing a wrench the wrong way can round off the bolt head or strip the arbor. Below is the actual mechanism behind it, how to tell which thread direction your saw uses without guessing, and a safe step-by-step blade change.

Why Reverse Threading Exists At All

A spinning blade doesn’t just cut — it also puts a small rotational drag on its own arbor nut, in the same direction the blade is spinning. On a standard right-hand-threaded bolt, that drag works against the “tighten” direction only if the blade spins one particular way relative to the bolt. If the blade spins the other way, the same drag actually helps unscrew a standard bolt a tiny amount every time the saw runs — and over hundreds of cuts, that adds up to a bolt backing itself out mid-cut, which is genuinely dangerous.

Manufacturers solve this with a left-hand-threaded (reverse) bolt on whichever side would otherwise self-loosen. The spinning motion then works to keep the bolt snug instead of walking it loose. It’s the same self-tightening logic used on the left-side lug nuts of some older rear-wheel-drive cars and on the left pedal of a bicycle — anywhere a spinning part could otherwise back its own fastener out.

Which Side Is Reverse-Threaded on Your Saw

The rule that actually matters: the arbor bolt is reverse-threaded on whichever side the blade sits on relative to the motor — because that determines the spin direction the bolt experiences.

• Blade-left saws (the blade is on the left side when you’re standing behind the saw looking at the front) — these are reverse-threaded. You loosen the bolt by turning it clockwise (to the right), the opposite of normal. Worm-drive style saws like the SKILSAW SPT77WML-01 and most other worm-drive circular saws are built this way.
• Blade-right saws (the blade is on the right side, which is the more common “sidewinder” layout) — these use a standard right-hand thread. You loosen the bolt the normal way, turning it counterclockwise (to the left). Most consumer sidewinder saws — DeWalt DWE575, Makita 5007MG/5477NB, Milwaukee 6390-21, and similar — fall into this group.

If you’re not sure which category your saw falls into, don’t guess from the brand — check the blade side yourself, or look at the arrow and “reverse thread” stamp usually cast right into the blade guard or the arbor nut itself. Most saws mark it there precisely because this direction is easy to get backwards.

How to Change the Blade Safely

Once you know which way the bolt actually turns, the swap itself is quick. Before touching the blade:

1. Unplug the saw or pull the battery — never rely on the trigger lock alone.
2. Engage the arbor/spindle lock (most saws have a button near the blade) so the blade can’t spin while you apply torque to the bolt.
3. Put on eye protection and gloves before handling the blade — carbide teeth are sharp even when the saw is off.
4. Retract the lower blade guard and confirm the saw is fully at rest.

With the spindle lock engaged, fit the correct wrench (usually included with the saw) onto the arbor bolt and turn it in the loosening direction for your saw’s blade side — clockwise for blade-left/reverse-thread saws, counterclockwise for blade-right/standard saws. It should break free with firm, steady pressure; if it doesn’t move, don’t force it harder in the wrong direction — double-check which side the blade is on first, since that’s the single most common mistake here.

Remove the outer washer, lift out the old blade, and check the new blade’s rotation arrow matches the direction stamped on the blade guard before sliding it onto the arbor. Seat the outer washer, thread the bolt back on by hand first, then snug it with the wrench — hand-tight plus a firm quarter-turn is enough; over-torquing an arbor bolt makes it harder to remove next time and can warp the washer.

Common Myths, Cleared Up

A few misconceptions come up often enough to call out directly:

• “All circular saws are reverse-threaded.” False — only the blade-side bolt on saws where the blade sits on the left uses reverse thread. Most sidewinder saws you’d buy at a hardware store use a completely standard thread.
• “Reverse-threaded means the blade spins backward.” No — thread direction and blade rotation direction are related but not the same thing. The blade always cuts with the teeth pointing forward at the bottom; the bolt’s thread direction is just chosen so the spin keeps that bolt tight instead of loosening it.
• “You can flip a blade over to reverse it.” Circular saw blades are directional — the tooth geometry only cuts efficiently one way. Flipping one on backward doesn’t “reverse” anything useful and will cut poorly or unsafely.

If the Bolt Won’t Budge

A stuck arbor bolt is almost always one of two things: it was over-tightened at the factory or on a previous change, or you’re turning it the wrong way for that saw’s blade side. Before applying serious force, re-confirm the direction. If the direction is correct and it’s just seized, a few drops of penetrating oil (like PB Blaster) left for 10-15 minutes, combined with steady (not jerking) pressure on a well-fitted wrench, resolves the vast majority of stuck bolts without needing an extension bar that could round off the head.

Maintenance That Prevents Future Problems

Clean the arbor bolt, washers, and blade with a resin-and-pitch remover after heavy use — built-up resin acts like glue and makes the next change harder regardless of thread direction. Inspect the bolt threads for burrs or rust before reinstalling; a damaged thread is what usually turns a normal blade change into a stuck-bolt problem. Replace a bolt or washer that’s visibly worn rather than fighting with it every time — a $3 replacement bolt is cheaper than a stripped arbor.

Frequently Asked Questions

Which Way Do You Loosen A Circular Saw Blade?

It depends on which side of the saw the blade sits on. Blade-left saws (most worm-drives) are reverse-threaded, so you turn the bolt clockwise to loosen it. Blade-right saws (most sidewinders) use a standard thread, so you turn the bolt counterclockwise, same as a normal bolt.

Which Way Do You Loosen The Bolt On A Circular Saw?

Same rule as above: check which side the blade is mounted on before turning anything. Guessing wrong and forcing it is the most common way people round off an arbor bolt.

Are Circular Saw Blades Reversible?

No. The tooth geometry is cut for one rotation direction only. Installing a blade backward doesn’t give you a usable “reverse” cut — it cuts poorly, burns the material, and is unsafe to run.

Which Way Do You Tighten A Circular Saw Blade?

Turn the bolt the opposite direction from loosening: counterclockwise to tighten on a reverse-threaded (blade-left) saw, clockwise to tighten on a standard-threaded (blade-right) saw. Hand-tight plus a firm quarter-turn with the wrench is enough — don’t over-torque it.

Conclusion

Reverse threading on a circular saw isn’t random — it’s there specifically to keep the arbor bolt from vibrating loose on the side where a standard thread would work against the blade’s own spin. Check which side your blade sits on, confirm the direction stamped on the guard or arbor, and the rest of the blade change is straightforward.