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Picking Open A Screw Lock

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GWiens2001

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Lock-Goblin-Gordon
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Post Sat Feb 27, 2016 12:42 am

Picking Open A Screw Lock

Picking A Screw Lock

Many of us have seen the screw locks before. Typically very cheap quality. But how do they work, and how do you pick one?

First, for those who are not familiar with the locks we are speaking of, they look like this.

Screw Lock 1.jpg


How do they work? Well, here is some of my famous artwork depicting the inside of the lock and key. No, am not an artist by any stretch of the imagination, but I can get the idea across.

Screw Lock 2.jpg


There are not many parts. The lock body, the shackle, the plunger/screw assembly and a spring. The key is a stepped tube with a threaded interior. No pics of the keys, because I got them without keys.

To open the lock, you put the key into the keyway until it stops, then start turning it. The screw inside the lock then gets picked up by the threads of the key. The key will wind down until the stepped part of the key contacts the face of the keyway. At that time, when you keep turning the key, the screw is drawn up into the key, pulling the plunger up, compressing the spring. Once the plunger is pulled back enough to clear the notch in the shackle, the shackle can be opened.

This is the edge of the plunger that functions as a locking dog that holds the shackle locked until the screw is pulled towards the keyway by the key.

Screw Lock 3.jpg


OK, how to pick the lock. After all, that is what we do here, right? :twisted:

First, estimate the diameter and thread pitch of the screw inside the lock. A flashlight can help.

Screw Lock 4.jpg


This one should be close enough. Note: You do not need to use a screw to pick this lock. The screw is so I can demonstrate partly what is happening inside the lock.

Screw Lock 5.jpg


Next, get some tubing that is about the same diameter in the inside as the outside of the screw.

Screw Lock 6.jpg


Crimp the tube about 1/4" to 3/8" (about 6-8 mm) up from the end. This is so the end is wide enough for the screw of the lock to fit, but that it narrows enough for the threads of the screw to catch and hold.

Screw Lock 7.jpg


Screw Lock 8.jpg


Now you can screw the tube onto the threads of the screw inside the lock. The screw used in the picture can help a little if you are able to correctly estimate the thread pitch, since it will start threads in the tube. Imagine this is inside the lock, the tube threads onto the screw of the lock perhaps half way the length of the screw. DO NOT thread the tube down so far that it bottoms out on the screw.

Screw Lock 10.jpg


Screw Lock 10.jpg


Put the end of the tube in a vise, and thread the lock onto the tube.

Screw Lock 11.jpg


When the tube is tight, then use a tool to pry the lock up away from the vise.

Screw Lock 12.jpg


As you lift the lock away from the vise, the plunger will pull away from the shackle. (The lock is unlocked for these pics so you can see).

Screw Lock 13.jpg


Screw Lock 14.jpg


Once the plunger is pulled away from the shackle a short distance, the shackle toe can be removed from the lock body.

Screw Lock 15.jpg


OPEN!!!

Hope this helps explain how these locks function, and how to pick them. Making a key would be as simple as cutting threads of the correct pitch in a tube, and add a washer partway up the tube that would allow the key to fit maybe 2/3 of the length of the lock body. Solder or epoxy the washer in place, and add a key bow so you have a little leverage to turn the tube. (It does not take much effort if there are decent threads in the tube). Will make a key someday, perhaps soon, and post the pics as an addition to this thread.

Gordon
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MBI

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Post Sat Feb 27, 2016 12:47 am

Re: Picking Open A Screw Lock

Gordon gets yet another post stickied.

Nice work Gordon, thanks for the great tutorial.
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Random

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Familiar Face

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Post Sat Feb 27, 2016 12:52 am

Re: Picking Open A Screw Lock

Thanks for the write up gordon. Ive seen a this type of lock before but never put to much thought into picking it. I just learned something new. Thanks
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macgng

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Contributor / I Fought Tooth and Nail to Acquire BO...
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Post Sat Feb 27, 2016 12:55 am

Re: Picking Open A Screw Lock

Not all of these types of locks are junk or made in india.... ;)

B&O Screw Key 1.JPG

B&O Screw Key 2.JPG

B&O Screw Key 3.JPG

B&O Screw Key 4.JPG

B&O Screw Key 5.JPG
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Papa Gleb

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Post Sat Feb 27, 2016 1:03 am

Re: Picking Open A Screw Lock

Awesome work as expected. Thank Gordon.
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macgng

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Contributor / I Fought Tooth and Nail to Acquire BO...
Contributor / I Fought Tooth and Nail to Acquire BO...

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Post Sat Feb 27, 2016 1:16 am

Re: Picking Open A Screw Lock

ah, yes! i did forget to mention in my previous post that GW is a genius!
Nibbler: The poop-eradication is but one aspect of your importance.
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Oldfast

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OldddffAASSTT the Spin Master Extraordinaire and American Lock Slayer
OldddffAASSTT the Spin Master Extraordinaire and American Lock Slayer

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Post Tue Mar 01, 2016 3:43 am

Re: Picking Open A Screw Lock

Simplistic brilliance! Great info here Gordon. Thanks! A well deserved sticky.
" Enjoy the journey AS MUCH as the destination."
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rphillips52

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Post Wed Mar 23, 2016 5:16 pm

Re: Picking Open A Screw Lock

In Britain, Hiatt and others made a heavy cast brass lock through 1960's. It takes a different size key from Darby handcuffs, and has a very strong spring, much stronger than Darby-style screwkey handcuffs.

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