Screw Size ID

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Mark-J
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Screw Size ID

Postby Mark-J » Mon Jun 10, 2019 7:39 pm

The following screw:

www.zoro.co.uk/shop/cromwell/prod/8x3-8 ... ZT1105056X

Just to make sure, the 4.2 x 9.5 numbers located in the brackets, that's the metric size equivalent of 4.2mm x 9.5mm?

Meccarroll
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Re: Screw Size ID

Postby Meccarroll » Tue Jun 11, 2019 5:32 am

Yes, the first number is the head size the second number is the length of screw.

When I first started in carpentry screws were in old style head and length. We would mainly use old sizes heads of 6,7,8,10 and 12 (yes no No 9's). And the length's were in inches or part inches. Now they are in millimetres.

Mark

Mark-J
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Re: Screw Size ID

Postby Mark-J » Tue Jun 11, 2019 8:21 am

Thanks for clarifying

telos
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Re: Screw Size ID

Postby telos » Tue Jun 11, 2019 4:32 pm

That's not quite right. At least for the metric part.
The first number is the *thread* diameter (4.2mm)
The second number is the threaded part length, from tip to base of the head. (9.5mm)

The imperial measure you probably know is (Gauge) x (Length)
Where Gauge is a measure of the head diameter *and* thread diameter.

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Re: Screw Size ID

Postby 9fingers » Wed Jun 12, 2019 8:38 am

A rule of thumb that seemed to hold true both for most screws and round headed bolts is that the head diameter is about double the thread diameter. There will always be exceptions of course!
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