Captive Screw

[stockdam]

I'm looking for ideas for removable captive screws. I have seen some before but can't remember where.

The screw/bolt is used to fasten an electrical connector to a captive nut in the mating connector. The screw is normally threaded at the tip but half way up the shaft it is reverse threaded (a thicker thread than the tip one). The screw fits into a collar in the chasis of the connector - the thread in the tip is smaller than the other thread and so it passes through the collar easily. Then you screw the reverse thread through the collar and out the other side - it then stops the screw from falling out again - to remove the screw from the collar you have to pull the screw up and turn it in the revese direction until the reverse thread comes out of the collar.

I hope this is clear. The 2nd thread maybe doesn't have to be a reverse thread but I think it is.

Has anyone seen a setup like this and if so where? Drawings or photos would be great.

 

[MadMango]

Looking for PEM fasteners?

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[stockdam]

I'm not sure if I understand how these fasteners work.

I wanted ones that are captive, can be tightened by hand and the screw can easily be completely removed by hand (but they won't fall out themselves).

 

[jistre]

PEM fasteners typically install in a hole via some sort of press and anvil. The pressure on the sheet it's being pressed into causes the sheet metal to flow into the specially designed nooks and crannies of the insert, holding it fast to the sheet.

What I'm not understanding completely is if the screw MUST be removed. Even if you remove the screw, you're going to leave behind the part of the fastening system that affixes the screw to its panel. Would it be enough if the screw portion of the fastener were spring loaded so that, when unfastened, the screw couldn't protrude through the sheet metal it's attached to? There are many of those types of fastener available at mcmaster.com

There's a lot of everything available at mcmaster.com, come to think of it.

 

[MadMango]

Are you looking for 1/4-turn dzus (zeus) fasteners?

Perhaps you have an image or there is an existing application that you can use to help explain what you are looking for.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[handleman]

The easily-removable captive screws I've seen only have one thread at the tip and the rest of the shank is about the size of the thread minor diameter. The panel or whatever should retain the screw is tapped to the same size as the threaded hole intended for the fastener. There's no need to have two different size threads and taps. Check catalog page 3019 of McMaster.com.

 

[GregLocock]

Look at the D plugs on the back of your PC. The little screws that nobody ever tightens up might give you an idea.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[unclesyd]

You might want to checkout Accurate Screw as they have a comlete line of captive screws.

http://www.accuratescrew.com/Captive-Screws.aspx