[Amps] What is it called?

[G3rzp at aol.com]

Will said:

"My guess is because 4-40 screws have more holding power than a 4-36 screw  
does. This is due to more threads in the thickness of whatever it's  
screwed into, either tapped material or a nut. Fine threads are always  
used in places where more holding power is needed in a thin section.  
Coarse threads are for thicker sections."


This is true up to a point. It's generally reckoned that if you have three threads engaged, that will give sufficient strength in most materials. However, softer materials benefit from using a coarse thread, because although the core and overall diameters are the same, there's more meat in each thread. All of which is why I tend to use Unified coarse threads (or even BSW!)in places where I'm using soft materials like aluminium, teflon, tufnol, polythene and even fibreglass. The last is very rough on tools, blunting them very rapidly, and carbide tipped tools are desirable. However, I haven't seen any carbide taps yet!!!

One point worth remembering is that plain carbon steel is harder than HSS (High Speed Steel) at low temperatures. HSS is used extensively where speed of metal removal is important, as in industrial machining, but for a lot of the stuff we do in home brewing, it's not worthwhile - certainly for taps and dies which are only used in hand tools.


73


Peter  W6/G3RZP (where it's warm and sunny, for you guys in the mid west and on the east coast!)