An Odd Screw

An Odd Screw

This topic has 5 replies, 4 voices, and was last updated 21 April 2020 at 08:22 by Bo’sun.

Viewing 6 posts - 1 through 6 (of 6 total)

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20 April 2020 at 20:29 #465958
Robert Dodds
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@robertdodds43397
Trying to tidy up and checking the contents of long forgotten boxes of assorted screws I spotted half a dozen of these today.

They are in steel, either 3/16 BSF or 2 BA with a Phillips type head but what is the purpose of the L.H. threaded portion just under the head?

Regards Bob D
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20 April 2020 at 20:29 #35867
Robert Dodds
Participant
@robertdodds43397
20 April 2020 at 20:53 #465965
Swarf, Mostly!
Participant
@swarfmostly
Hi there, Robert,

One purpose of screws like that was/is to secure loudspeakers to their baffle board. The coarse left-hand screw engages the plywood baffle board and the machine screw portion takes washers and nuts to secure the loudspeaker. Tightening the machine screw nut also, because of the left-hand thread, tightens the wood-screw part.

Best regards,

Swarf, Mostly!
20 April 2020 at 21:13 #465971
Robert Dodds
Participant
@robertdodds43397
Swarf,

I think you've "nailed it" The top bit does look remarkably like a wood screw thread.

Regards Bob D
20 April 2020 at 22:01 #465974
Robert Atkinson 2
Participant
@robertatkinson2
Not just loudspeakers, but that as a common appliction. Used in all sorts of wooden cabinets with mechanical fixings. The one pictured is a bit long for loudspeakers.
There are similar looking wood screws with a different "thread" on the shank that is supposed to reduce the driving torque when installing but keeping the screw tight when installed..

See also pronged tee nuts, not the type used in machine tables.

Robert G8RPI.
21 April 2020 at 08:22 #466022
Bo’sun
Participant
@bosun58570
Definitely looks like left over flatpack hardware. Check your Swedish furniture.
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