Anyone tell me the correct definition for the length of a countersunk screw that's 5mm long overall, comprising a 3mm threaded section plus a
2mm deep countersunk head? Is it a 5mm or a 3mm screw, or even something else?MTIA
In message , Kevin Poole writes
Thanks,
I should have asked originally, is that the same with a pan head too?
For all screw head types, the length is measured to where the surface of the wood/metal is supposed to go. This is usually the widest diameter of the head. So if you have a round-head screw with 5mm thread, and a 3mm diameter dome on top, then that's a 5mm screw. Similarly, consider one of those screws that Wikipedia describes as oval, and whose real name I can't remember; a 5mm version would be
3mm thread, 2mm countersinking, and 2mm dome on the top.
Thanks again, it's what I was expecting, hadn't thought of the 'oval head' case though.
=2E.. and the follow up trivia question: In a 1/2" BSP pipe. What measurement of the pipe is actually 1/2"?
Robert
Strangely enough I've been measuring a few bolts to put them back in the right draw but my M3 M4 & M5 bolts seemed to be measured as the actual length of the thread of the bolt i.e excluding the head, but then these are what I'd call bolts in that they need nuts rather than self 'screwing' although the catalogue calls them screws. I've a box of No. 8 2 inch slot round black japanned woodscrews that also appear to follow this excluding the head measurement. The head being aboit 1/10th of an inch.
Unless you choose to believe ...... ;-)
Raised countersunk IIRC
The diameter of the 'hole down the middle', which is really the important parameter rather than the outside diameter :-)
BSP sizes relate to the bore of a wrought iron (2.5" and under) or cast iron (3" and over) pipe that will take the thread on the outside.
Colin Bignell
Yes, AKA "instrument head". Length measurement is as for a standard CSK screw, as if the raised part of the head were not there.
5mm is an extremely short screw, sure you don't mean 5cm?
A screw has a head and is threaded along all its length. A bolt has a head, followed by a plain shank, followed by a treaded part at the bottom. A bolt is usually used in a sheer situation, as the shank is not reduced in diam. by the threads. A screw is measured from the surface that it has been set on/in and a blot is measured by the length of the plain shank plus the head if it was a countersink bolt. This is so that the bolt can pass right through the joint allowing a washer to be fitted, that covers the small amount of shank that protrudes.
Dave
They are called "raised head screws".
Not nesser-celery, it might be a grub screw...
:-) ITYM "shear".
Uh? The length of bolts is measured exactly as for screws, including the threaded part of the shank. I've never encountered anyone measuring bolts only by the plain part of the shank.
Agreed :-)
:-( see below.
That should have read... and a bolt is measured by the length of the plain shank plus the head if it was a countersink bolt.
This is done so that the calculated thickness of a metal joint in shear has all shank through it. Any protruding shank can have a washer that allows the nut to tighten down on it, without being thread bound.
In my history of engineering, a bolt was always specified as having an un-threaded shank of length quoted. When I was an apprentice fitter, we measured boils by diam and plain shank. They were Whitworth and the plain shanks went up in 1/4 inch increments.
Thanks for the corrections Andy, but I had 2 grand daughters making lots of noise when I wrote that.
Dave
Agreed but possible. Using your senario,
then a 2cm countersunk head is VERY big ;-)
HTH
John
In message , Scabbydug writes
Nope definitely 5mm.
Which is why I'd hammer a screw to start it off but not a bolt. Well unless I was attaching it to some students neck :)
Not if it's a 3mm or less diameter machine screw. 5mm is a normal sort of length, 50mm would be exceptional.
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