Slightly OT: Left hand screw

[fusker]

Only time I ever saw a left hand screw: On my Skoda Felicia (smallish czek/german car) a separate pulling hook is provided. This cold winter I had to use it, found it allright in the tool box, tried in vain to screw it into the front bumper hole. WTF? Try again and yet again. Had a close look: Left hand thread! There even was an illegible drawing on a dime sized label attached to the hook.

Why would that be? Any suggestions? Have any of you seen L/H screws (and I don't mean L/H thread in lead screws, bicycle pedals and other special applications)?

Can't post a photo cause I eventually managed to break the *!@¤ screw. Have to drill it come spring. Regards, fusker

 

[David Utidjian]

Why would that be? Any suggestions? Have any of you seen L/H screws (and I don't mean L/H thread in lead screws, bicycle pedals and other special applications)?

My only guess for an L/H screw in your application is that they didn't want you screwing anything else in there.

L/H screws are almost always "special applications"... that is to say, there is no reason to use an L/H screw unless the application requires it. Some other common applications ("special" or not) lug nuts on some US cars, threads on the L/H side of a grinder shaft, turn-buckles, jacking screws, knock-off hubs (wire wheeled British sports cars). Out of all the applications I can think of at the moment the L/H lug nuts on some older US cars is the only one that doesn't make sense to me.

-DU-

 

[L Vanice]

I have seen left hand screws used on all my electric/battery hand drills with reversing switches. The drill chucks are threaded right hand, so the spindle has a left hand tapped hole down the center. The left hand screw is then driven down through the center bore of the chuck after the chuck is tightened onto the big right hand thread (3/8-24 or 1/2-20, usually). The purpose is to prevent the chuck from coming loose when running in reverse. There is a very sound engineering reason for the LH screw. The drills I had in my younger days did not have reversing switches, so they did not have the LH screw.

Left hand gas fittings are used for acetylene gas tanks, torches and regulators so they won't get mixed up with oxygen fittings. The LH threads are a safety measure.

From the description, I don't know why a tow hook would be fastened with a left hand screw. There should be a valid engineering reason, like safety or mechanical function. I don't suppose the Czek or German engineers would do it as a joke.

Larry

 

[RODELU]

L/H thread is there to make sure you use the pulling hook in the tool kit, not some off-the-shelf part that doesn't meet the specs for towing.

 

[Clews Machining]

Every Volkswagen I've ever been around has the same left hand threaded tow hook. I would be inclined to agree with RODELU as for the reason behind it.

 

[fusker]

Bingo!

L/H thread is there to make sure you use the pulling hook in the tool kit, not some off-the-shelf part that doesn't meet the specs for towing.

I think you got it, Rodelu, thanks, hadn't thought of that.
But on the other hand, when I tried to tighten the screw, it broke clean off. Very soft steel and badly engineered. So almost anything woulda been better.
Going to make a permanent hook as a replacement.

 

[Sea Farmer]

A malleable towing hook would be safer than a hard brittle one, as it would deform under excess stress rather than snap off and send a projectile towards the towing vehicle.

On the other hand, one that breaks off when tightened is no good either. Unless you over-tightened with a jimmy bar? It doesn't need to be in super tight, as the longitudinal pull of the tow should hold the threaded portion in place. No reason for it to twist while under force.

 

[swamp dweller]

Had a Dodge p/u in the early 70s that had left hand threads on the wheels only on the left side of the truck if I 'member right. Drove me crazy trying to change the tire 'til I took a closer look at the threads. Of course my eye sight was a lot better then.

 

[gorrilla]

Had a Dodge p/u in the early 70s that had left hand threads on the wheels only on the left side of the truck if I 'member right. Drove me crazy trying to change the tire 'til I took a closer look at the threads. Of course my eye sight was a lot better then.

Drove you crazy? Short trip? (I'm an equal opportunity harasser. I'll mess with anybody, anytime. Know em or not. Feel free to retaliate, in good fun of course,)

 

[9100]

One evening we were hanging around a friend's garage while he tried to change a tire on a home made motorcycle trailer. He just couldn't get the lug nuts off, trying longer and longer pipes on the wrench handle and pulling until he turned purple. Eventually an old timer came along, listened to Jerry cuss a bit, and only said "It's a Chrysler, aint it?" Of course, Jerry then had to figure out how to loosen nuts tightened to goolgeplex to the N foot pounds.

Bill

 

[Mike C.]

"L/H thread is there to make sure you use the pulling hook in the tool kit, not some off-the-shelf part that doesn't meet the specs for towing."

Boy, we could show them, all ya need is a left hand die and a bolt. heheheh.

 

[register]

There are many applications for left-hand threads.

People already mentioned things like wheels (an application that seems to have fallen out of favor) and drills. I have seen a left-hand thread that held an impeller on a pump shaft.

Another common use is on a turnbuckle.

Henry

 

[Mike C.]

Most all multi-stage turbine pump shafts are left hand thread. Really bad idea to start one of those with the rotation wrong! Tends to blow itself apart in short order.

 

[gas pumper]

The silver lining to the OP is that as he goes in with his right hand drill to remove the broken stub, the piece will turn itself out, unless they have road salt in Denmark.

 

[slnielsen]

My girlfriend had a Seat Ibiza, part of the VAG group as well, which had the exact same hook.. Took me a little while to figure it out freezing in 2 ft. of snow..

And yes.. We use a lot of salt on the roads here..
That's why we like to import old US cars from CA.
The ones that were here for 50 years has rusted away..

Best regards
Søren

 

[9100]

Twisted ropes and cables tend to untwist under tension. Maybe they didn't want the hook unscrewing itself. OK, I admit that is a long stretch to think up something to post.

This is hearsay, but have been told that in New York City municipal light bulbs have left hand threads to keep people from taking them home.

When my sister and I were little, our father kept his 1898 Marlin pump shotgun broken down so we couldn't get in trouble with it. The barrel has a left hand thread attaching it to the receiver. I have no idea why, unless it was to keep little kids from putting it together and shooting their friends.

Bill

 

[PixMan]

My old BMW has a little cap snapped into the bumper cover on either end of the car where you can attach the tow hook that lives in the trunk (boot) lid mounted toolkit.

It's a right hand thread, and I've had to use it once when the alternator failed and I failed to analyze that I had driven some 30 miles...on battery power.

My issue with these tow hooks isn't the thread or that they are there at all (none of my American-made cars ever had them.) My complaint is the location. Why do they put the mount off-center?

 

[fusker]

To save Skoda's reputation

On the other hand, one that breaks off when tightened is no good either. Unless you over-tightened with a jimmy bar? It doesn't need to be in super tight, as the longitudinal pull of the tow should hold the threaded portion in place. .

The screw was abt. 11 mm (less than 1/2 inch) and I had to use a jemmy as the threads were a bit rusty. Only a 1 ft. jemmy in the hands of a non-bodybuilder. Should not break a normal eye bolt that size. Design was bad, though: Smallish threaded part and large shoulder with no stress relief whatever. Broke at he shoulder, of course.
Threads were non-standard so it would be difficult to find anything un-original to fit (apart from the L/H) so yes, one had to use the original hook. Maybe the good Skoda-engineers thought it better to ruin the hook than to pull off the bumper!
Thanks for all your suggestions.
Regards, fusker

 

[fusker]

'Towing' a car in Germany

My issue with these tow hooks isn't the thread or that they are there at all (none of my American-made cars ever had them.) My complaint is the location. Why do they put the mount off-center?

I believe you must use a bar to 'tow' a car in Germany (and Denmark). The front end would be attached to the 'pulling hook' in center of the rear end. This would make it a little bit safer if the front car crashes?
Thanks for your comment, I had wondered abt the location.
Regds, fusker

 

[WizardOfBoz]

When I was in high school, my Dad's company won a contract with the US Govt to supply industrial lawnmowers. 700 of 'em. I got the job of stamping "LH" on 700 shafts with hand stamps and a hammer. Not too bad a job, just boring. Anyway, lawnmower shafts sometimes have LH threads to keep the nuts and the blades from spinning off.

J