Lefty hefty, righty lighty: reverse threading in the workplace

[Philbert]

The Army's tank hauler the Heavy Equipment Transporter (HET) uses left hand threads on the trailer on inner side, if I remember correctly.

 

[fos373]

i have a radical race car in which the centerlocks are reverse thread on one side of the vehicle, normal on the other......

 

[Dingleburry]

Anything that spins cw and is fastened with a threaded fastener.
Left hand threaded are used in rotating machinery where the motion or torque would losen conventional bolts/screws.

Most pump impellers are reverse thread.
Collet's used to join extruder screws to gearbox are left hand thread.
Turnbuckles.

 

[Dingleburry]

i have a radical race car in which the centerlocks are reverse thread on one side of the vehicle, normal on the other......

The passenger side reverse thread?
So the torque dosent losen the side spinning cw.

 

[4x4gearhead]

Most mid to large platform hydraulic cylinders found on excavators have a left handed jam nut against the right hand threads on the piston. I see this quite often.

 

[Tanro]

Chuck nut on rotor lathes.

 

[bonneyman]

Here's a question, guys: Are left hand threads the same pitch and TPI as right hands threads, just backwards? Or, are they unique to lefties?

 

[Mgdoug3]

I have only bought one left handed tap. It is a 1/2" by 13, same as a right threaded bolt. I'm guessing they come in the same pitch but can't say for sure based off one tap.

I have that tap since I stripped out a left handed nut which I though was right handed. Couldn't find the right tap but was able to drill out a tap and retap it until the correct tap came in. That's how I learned about left handed threads on a planter.

 

[Millwrong]

Here's a question, guys: Are left hand threads the same pitch and TPI as right hands threads, just backwards? Or, are they unique to lefties?

Yes, everything is the same, except the direction of the helix.






As far as where to find LH threads, I can't think of anything new. Acetylene regulators have been mentioned, but I think its worth adding that any fitting when being used to carry flammable gas will typically be in LH thread. Hopefully, it'll be identified by cuts on all 6 corners of the hex portion:

 

[phule]

Just got flashbacks of a ford aspire pass rear spindle nut.*shudder* found out the hard way righty loosey lefty tighty.

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[bonneyman]

Anything that spins cw and is fastened with a threaded fastener.
Left hand threaded are used in rotating machinery where the motion or torque would loosen conventional bolts/screws.

That's kinda the assumption I was leaning towards. Makes sense - you'd want normal operational spinning to tighten a fastener, not loosen it.

 

[gnpenning]

Propane tank, is another flammable tank.

 

[Milton Shaw]

On wood lathes that have an outboard turning option the tread on the back of the spindle, the faceplates and treads are reverse.

 

[MBfreak]

Quote
True knock-off wheels are LHT on the passenger side.
Unquote.
Knock off spinners come in all manners-
Left side , left or right thread
Right side , left or right thread.

This was a question in a german classic car magazine some 25 years ago.
Part of a 25 q competition.
There were 1000´s of 24 right answers, but only around 40 25 pointers
The spinner was the knockout.
I was one of the 25ers, but not the lucky winner, who got a very complete set of Gedore tools.
I got a fancy set of WERA screwdrivers.

Ola

 

[Dusty-NZ]

I just made several left thread wheel nuts for my '37 Chev pickup. (it was fun )

 

[jeffmoss26]

I deal with it daily...key machines are reverse threaded.

 

[WWheeler]

I work on reverse threaded stuff every day in an industrial setting. Any part of a machine that rotates counter clockwise relative to the fastener has to be reverse threaded or else it would never stay tight.

 

[6PTsocket]

Hmm. Didn't realize that.
Most BB fixed cups I've worked on were real tight - almost as if you were cross threading them. Threads on both parts were clean, lube didn't help much. Maybe they made them slightly off to deal with the loosening problem?

There is a thread style called a locking thread. I am not referring to the deformed locknuts. This is either on the bolt or threaded part that recieves it or both. I am not exactly sure how it is done. My old Ajax/Walker,floor jack used it on the pump mounting bolts. There were no lock nuts needed. That must be what you have. Hard to turn all the way but not stripped or cross threaded.

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[PFSard]

Hmm. Didn't realize that.
Most BB fixed cups I've worked on were real tight - almost as if you were cross threading them. Threads on both parts were clean, lube didn't help much. Maybe they made them slightly off to deal with the loosening problem?

I've only had a problem the first time I worked on a bottom bracket. Didn't realize that the fixed cup was a left-hand thread!! Going back together was relatively smooth on any that I've done.

Any particular brand of bike that the fixed cups were real tight, even though threads were clean and lubed?

 

[4xdog]

A left hand threaded thing of beauty -- a vintage Borrani wire wheel with knockoff nut.

And as part of the common language that separates us, our British friends will typically call this a knock-on nut. Can't remember what the Italians call 'em...

 

[TRX]

Here's the knockoff on a D-type Jaguar at Goodwood a few years ago:

Great googly moogly! That's a ton of weights for an off-brand truck tire. I would consider any street car tire to be defective if it needed that much. And I'd be unhappy about a racing tire that needed more than a bit.

It could be that the rim is that much out of balance, but for a Real Race Car Part(tm), I'd want to know why, and then I'd at least static balance the poor thing if it was some rare part that couldn't be replaced.

 

[bonneyman]

I've only had a problem the first time I worked on a bottom bracket. Didn't realize that the fixed cup was a left-hand thread!! Going back together was relatively smooth on any that I've done.

Any particular brand of bike that the fixed cups were real tight, even though threads were clean and lubed?

It's been a long time since I worked on any of those bikes, but as I recall the Peugeot and Schwinn steel-framed bikes were almost always a bear.

 

[manioso]

Briggs & Stratton engines of 2hp to 5hp had a left-hand thread on the crankshaft if rope started, and a right-hand thread if using a recoil starter. True for both cast iron as well as aluminum block engines.

 

[bonneyman]

Briggs & Stratton engines of 2hp to 5hp had a left-hand thread on the crankshaft if rope started, and a right-hand thread if using a recoil starter. True for both cast iron as well as aluminum block engines.

Interesting! I'll have to check out my 3HP B&S lawn mower.

 

[MikeRock]

There is a gear (properly called a "wheel") in mechanical watches that frequently has a left hand screw. Due to the rotational reasons already discussed. Sometimes the screw head is marked with three lines -- the slot for the screw driver and additional lines on each side. That might be a symbol to look out for.

 

[drewsifer714]

Which ones? I've been working on walk-behind mowers since the 1970s and I have never come across a LH thread on a crankshaft bolt. Briggs & Stratton, Tecumseh, Kawasaki, Honda engines are what I have worked on and they've all been standard RH threads.

Couldn't tell you now, it was years ago. But with you saying that I wonder if the one I broke and thought was reverse was actually just seized. I do recall it breaking though, and at the time I thought that was the reason.