US/English thread + servo driver

Hi all,
First question: --------------- being a citizen of an european country I do not know much about the US threads standards for screws and nuts. As I have to use them from time
to time, I wonder if some of you guys can make some light on the different non-metric systems. As far as I know, there are three basic systems: UNC, UNF and Whitworth. I've been told the last one is almost abandoned, and I often come across definitions of screws without any UNC or UNF before. Does this mean that one of these systems is more used than the other, that it's not needed to mention it? Are there any tables of these threads available on the net?
Second question: ---------------- Is there anybody who can point me in the right direction to find an RC Servo control circuit which can be used to move a servo by an altimeter?
Thank you in advance for your help!
Stefano Figoni www.sierrafoxhobbies.com
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snipped-for-privacy@sierrafoxhobbies.com wrote:

These refer to the "fine" or "coarse" thread series of the screws.
If the actual thread size is given (such as 1/4-20 or 1/4-28), that is enough information to select the matching nuts, taps, dies, etc. (The first number is the diameter in inches and the second is the number of threads per inch.)
-dave w
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US
time
before.
other,
UNC (Unified National Coarse) is the coarse thread series for bolts and machine screws. UNF (Unified National Fine) is the fine thread series for bolts and machine screws. The USA also has a thread standard for "pipe threads" (National Standard Taper Pipe Thread or NPT).
This page covers a reasonable range of sizes of UNC and UNF threads:
http://www.rfcafe.com/references/general/tap_drill_sae.htm
My only experience with the Whitworth system is in older automobiles from the UK. I don't believe it was ever commonly used in the USA, and as you commented, I also believe that it is essentially obsolete.
This page gives some history of obsolete British thread systems, including Whitworth:
http://www.enginehistory.org/british_fasteners.htm
-- Erik
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Nice table of sizes, but note that the "drill diameter" column is the size to drill for a TAP, not for CLEARANCE. i.e. a 1/4-20 screw needs a 0.201 hole for tapping, but obviously a 0.250 hole for tight clearance.
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I used with success the following circuit.
http://www.kestii.go.ro/Electronica/gadgets/servo3.htm
I just replaced the 2.7k pot with two ones switched by a small relay.

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Thank you all for the answers, it is much clearer now! Stefano Figoni www.sierrafoxhobbies.com
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