What is the "extra thread" on this screw?

Reply

  #1  
Old 07-21-14, 12:58 PM
M
Member
Thread Starter
Join Date: Jul 2014
Location: Denmark
Posts: 2
Received 0 Votes on 0 Posts
What is the "extra thread" on this screw?

I wonder what the idea is behind these extra thread like ridges above the actual thread. Can anybody tell me?

See attached image.
 
Attached Images  
  #2  
Old 07-21-14, 01:14 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,841
Received 856 Votes on 784 Posts
Supposedly, once the wood threads are fully threaded into the wood, those other threads "rasp off" any fibers that are sticking straight up out of the hole so that the bugle head can countersink itself into a clean hole without any of those fibers building up underneath the head. It's kind of similar to a composite screw in that way.
 
  #3  
Old 07-21-14, 01:19 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,489
Received 1,422 Votes on 1,315 Posts
Those look like self-countersinking cabinet hanging screws.
 
  #4  
Old 07-21-14, 01:52 PM
M
Member
Thread Starter
Join Date: Jul 2014
Location: Denmark
Posts: 2
Received 0 Votes on 0 Posts
Thanks. Let me just understand what a composite screw is then From Googling, I think it is a screw for use on composite materials (eg PVC). I guess on PVC self countersinking is not as straight forward as on wood. A cone shaped head will not simply press itself into the material, or if it does, it won't look nice. Therefore the top part of the screw must have some ridges to remove the material at the point where the head will sit.

I haven't done much carpentry, so I am kind of guessing / assuming. But am I right?
 
  #5  
Old 07-21-14, 01:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,489
Received 1,422 Votes on 1,315 Posts
Therefore the top part of the screw must have some ridges to remove the material at the point where the head will sit.
Yes..... that is correct.
 
  #6  
Old 07-21-14, 02:17 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 21,112
Received 4 Votes on 4 Posts
Sorry, sorta have to disagree with the explanation...at least according to GRK. http://www.grkfasteners.com/index.php/en/products/r4

Those extra twisted cutting threads on the shank are to slightly enlarge the hole for the unthreaded portion of the shank. This allows lower driving torque and gives more draw strength. Like drilling a slightly oversized hole in one piece, to allow the screw head to firmly clamp that piece down to the other piece. RK calls them CEE thread.

The part directly under the head (as shown on the GRK fastener) will cut away any stray fibers and allow a clean countersink. Your's doesn't have that feature.
 
  #7  
Old 07-21-14, 04:04 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,841
Received 856 Votes on 784 Posts
Same difference... they rasp the hole bigger for some reason or another. LOL (But now that I think about it, I guess that's not the same as the composite screws at all. Those threads are right under the head of the screw and actually grab the loose fibers and suck them down into the hole.)

I imagine from the picture that the bugle head does have the little ridges that help countersink the head. But I have a good imagination.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: