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stud thread tip
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Ray White



Joined: 02 Dec 2014
Posts: 3173
Location: Derby

PostPosted: Fri Oct 05, 2018 9:49 am    Post subject: stud thread tip Reply with quote

Some studs have an equal length of thread but we will all have noticed that many studs have threads of unequal length - but it may seem unclear which end screws into the block/head etc.

I have always understood that the short end screws into the permanent part and the nuts therefore screw onto the longer thread.

I believe this to be normal practise but it would be interesting to find an exception to the rule, if one exists.
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Miken



Joined: 24 Dec 2012
Posts: 266

PostPosted: Fri Oct 05, 2018 10:26 am    Post subject: Reply with quote

Im sure There is a formula for this (I don't know it) but when I was a machine toolmaker apprentice many years ago my mentor taught me that when screwing a steel stud or screw into steel,the rule of thumb on the shop floor was, the depth of thread that was required was 1x the diameter of the thread. In iron you need 1.5 times and in aluminium alloy 2x.
Any amount of thread longer than this gives no benefit. You could have a M8 stud with 10 meters length of thread screwed into a component. It won't be any stronger and will still fail at the same tension as the other examples above.
This is why standard nuts are the thickness that they are. In fact they are approximately equal to the core of the thread which is actually smaller than the outside diameter. Making them thicker/longer makes them no stronger.
So I would agree with Ray that usually the short thread will be the one that screws into the component, head, cylinder block or whatever.
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MikeEdwards



Joined: 25 May 2011
Posts: 1834
Location: South Cheshire

PostPosted: Fri Oct 05, 2018 10:27 am    Post subject: Reply with quote

That does seem to be the case on my seventies Vauxhalls, but in those there is an easier way to tell - the end that screws into the block is UNC, and the "other" end is UNF. Seems like all the holes on that block are coarse threaded, whether they'll have a stud or a bolt/screw in them.
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Penman



Joined: 23 Nov 2007
Posts: 4080
Location: Lancashire

PostPosted: Fri Oct 05, 2018 7:38 pm    Post subject: Reply with quote

Hi
Unless the holes in the block go through to a cavity, can't you tell by measuring the depth of the hole?
The blank, threadless, section of the stud has to coincide with the head and not protrude above it
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Miken



Joined: 24 Dec 2012
Posts: 266

PostPosted: Sat Oct 06, 2018 8:44 am    Post subject: Reply with quote

The depth of thread in the tapped hole should be greater than the length of thread on the stud being fitted so that it doesn't bottom out . The stud should be tightened lightly down to the plain shank . If done up too tight the plain shank will raise a burr around the joint face which will then have to be removed usually by oil stoning followed by lightly countersinking out to the diameter of the thread.
Another hazard not commonly encountered with studs but I've seen it many times with screw applications usually on old motorbikes is hydraulic fracturing caused when gasket sealant or grease gets into a blind hole and cracks a casting and often forces a big lump off the side or out the bottom of the hole.
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