An odd one .

[Charles in Aus.]

While rifling around looking for old solder the other day I found a container of old brass screws and bolts . I grabbed a few for the base of the lightshade I was repairing and caught a glimpse of these.

Six left-hand thread brass screws.
I've never seen the like before. All I can think of was that they might have been used to fix instruction or name plates to something . If tampering was an issue it's hard to understand why rivets weren't used instead .

 

[scootergmc]

Screws turn the other direction in the southern hemisphere.

 

[urbancase]

I ran into left hand threads on one of my kids bikes when they were young, to repair I bought a 7-16 fine thread lace hand tap. However not the small, bought be for something that rotates to stay tight. Not sure what.

 

[unc]

Left hand threads were commonly used in Britain until recently. Quite often, adjusters and adjustment screws would be mixed left and right hand threads so motion of adjustment was consistent. In the early days of manufacturing, thread systems were not standardized. Each manufacturer used their own system, and it could be right or left handed. If the Brits used a left hand thread, there was usually a good reason. Elliot milling machines, English made, use the same hand motion for all three table lock downs. This involves two RH threads, and one LH thread. Bridgeport mills, US made, use two motions one way, and the third is opposite because all three lock downs use a RH thread.
Those screws look like a BA or CEI thread, possibly from a bicycle or motorcycle.
Long time back, Dad bought an old English made cast iron machinery seat with the spring still attached at an auction. It had the usual flush plow type bolt and square nut holding it together. I tried every wrench on the place, and several types of weasel P on it, trying to get it apart. No luck. I talked to my machine shop teacher at school about it, and he suggested it might be a left hand thread. Sure enough. It came off easily when I turned it the right (left) way. Lesson learned. In my working life as a machinist, I've often come across LH threads on European made machinery. Keeps you on your toes. unc

 

[sms]

They look like faucet washer screws. Could they be for a similar application so they don't loosen when faucet is turned?

 

[ss55]

They look like faucet washer screws. Could they be for a similar application so they don't loosen when faucet is turned?

Yes, some faucet sets both turn clockwise to open the taps. Some sets the hot tap turns counterclockwise while the cold turns clockwise to open. Replaceable cartridge valves make life easier.

 

[Stephen Newell]

While rifling around looking for old solder the other day I found a container of old brass screws and bolts . I grabbed a few for the base of the lightshade I was repairing and caught a glimpse of these. View attachment 139772

Six left-hand thread brass screws.
I've never seen the like before. All I can think of was that they might have been used to fix instruction or name plates to something . If tampering was an issue it's hard to understand why rivets weren't used instead .

Usually left handed screws are used on something that is turning in use. If it was right handed thread it would have a tendency to unscrew from the rotation.

 

[Dingo3]

Chrysler used left hand threads on the drivers side wheels up into the late 60s. I’ve seen many a busted off stud and irate owners who found out the hard way.

 

[Brian G. NY]

Chrysler used left hand threads on the drivers side wheels up into the late 60s. I’ve seen many a busted off stud and irate owners who found out the hard way.

Some other automakers did the same.
I have a few LH studs and nuts from old Dodge and Plymouth cars in my "stash".
I once had both a '47 Dodge and a '48 Plymouth.
As I recall, the Dodge used studs and the Plymouth nuts.

 

[Brian G. NY]

I ran into left hand threads on one of my kids bikes when they were young, to repair I bought a 7-16 fine thread lace hand tap. However not the small, bought be for something that rotates to stay tight. Not sure what.

The pedals often had LH threads on one side.

 

[Brian G. NY]

Yes, some faucet sets both turn clockwise to open the taps. Some sets the hot tap turns counterclockwise while the cold turns clockwise to open. Replaceable cartridge valves make life easier.

That is a very likely use for them....never saw it myself but it makes perfect sense.

 

[Russ from MN]

Did they make small screws in Whitworth threads too? I drive Triumph motorcycles, and my first 2 were Whitworth. Now they are modern, metric!

 

[kencombs]

Some other automakers did the same.
I have a few LH studs and nuts from old Dodge and Plymouth cars in my "stash".
I once had both a '47 Dodge and a '48 Plymouth.
As I recall, the Dodge used studs and the Plymouth nuts.

I could never confirm which used which. Just when I thought I'd figured it out, I bought a 56 Dodge pickup. Still working on that on as a matter of fact. One of the first things I did was drill out the tapped holes in the axles/hubs to accept pressed in studs to replace the bolts.

Mainly because I wanted to use non-stock wheels which will not have the hole for the pilot pin used with bolts. And I hate installing bolt one wheels without that pin, which all Mopars used.