> what about the 5mm x 1.75. It appears to be a
>non-standard size and what is it used for. Is it correct, the standard size
>I can find is 5mm x 0.8
Alan - I think this must be a typo! I can't imagine a 5mm thread with such
a coarse pitch. The Whitworth (BSW) and Unified Coarse (UNC) thread forms
are about the coarsest in general use, and you need to go to a much larger
diameter before getting that large a pitch in those thread forms (7/16" x
14TPI or about 11.07mm x 1.81mm). The smallest diameter ISO threadform with
1.75mm pitch is indeed 12mm. If the 5mm diameter is assumed correct, the
only pitches called out in the standard are 0.8mm (coarse) & 0.5mm (fine).
Neither of those looks an obvious candidate for a misprint as 1.75mm.
Next possibility is that at least part of the pitch is correct, and the
diameter is a typo. Perhaps the pitch should be 0.75mm? That allows 4.5mm x
0.75mm (coarse, non-preferred), or any of the constant-pitch fine series as
follows: 6mm x 0.75mm, 7mm x 0.75mm (non-preferred), 8mm x 0.75mm, 9mm x
0.75mm (non-preferred), 10mm x 0.75mm, or 11mm x 0.75mm (non-preferred).
Perhaps the pitch should be 1.25mm (maybe a more likely visual error than
the 0/1 switch above). That would offer 8mm x 1.25mm (coarse), 9mm x 1.25mm
(coarse, non-preferred) and the fine versions 10mm x 1.25mm, 12mm x 1.25mm
or 14mm x 1.25mm (non-preferred).
Looking at all the possibilities, I feel that it would be unlikely for a
non-preferred size to be chosen. Also, fasteners are much more readily
available in the coarse threads, so I think my vote would go to 8mm x
1.25mm as the most likely candidate. It's the only coarse thread
description that presents a ready visual confusion with 5mm x 1.75mm,
especially if handwriting was involved anywhere along the line.
Sorry, but I can't guess what the tap might be used for! Factory, do you
need to fit a M8x1.25 fastener into a tapped hole anywhere on the airframe?
cheers
Rowland
PS: I have a handy little spreadsheet comparing common threaded fastener
sizes. I find it very useful when identifying bolts & nuts, and when
deciding which size to use. It covers BA, BSW, BSF, UNC, UNF, and ISO
coarse. If anyone wants a copy, please ask in private email. You can have
Resolve, Excel V5, SYLK or tab-text formats. All except the tab text will
retain the pretty colours which identify different thread families. SYLK &
tab-text can be read by any spreadsheet application, and as they are both
plain ASCII text files can be sent by email without problems. The Excel
file _should_ travel OK too, but if the encoding/decoding capabilities of
your mail client & mine are incompatible, there could be problems.
... that's Rowland with a 'w' ...
|