I think it's easier, particularly these days, to get tripped up by so many
variations of fine threads since there are so many in use.

Machine parts ain't what they used to be.. now that there are often a mix of
metric and inch fasteners, very commonly, it seems.

It's not too difficult to distinguish 1/4, 5/16 and 3/8 coarse threads from
6, 8 and 10mm threads by eye and fine threads of each are a matter of
recognizing the proportion between diameter and pitch.. but when the threads
start getting finer, such as on machine parts, assumptions and guesses are
more likely to lead to rework.

Jumping around from general hardware to optics and electronic parts threads
can get complicated.
In addition to machine-formed threads, there are numerous applications where
threaded parts are diecast, leading to more visual examples.

Gilda - Roseanne Roseannadanna had it right..

--
WB
..........


"Bob La Londe" wrote in message
...
Ok... I was kinda judgemental with somebody recently about figuring
out a thread. It bit me in the butt today. I was converting a belt
drive Z axis on a CNC router to a direct drive with a helical
coupler. I needed to replace the pulley on the ballscrew with a
bushing to fit the helical coupler. The pulley was also the nut that
puts pressure on the fixed bearings for the lead screw. Being a
chinese machine I assumed it was metric, but after fighting with it I
don't have a clue what it was.

It definitely was not 8x1.25. I didn't have an 8x1 tap and I couldn't
find my thread gage. My 5/16 x 24 tap threaded easily into the pulley
about 7-8 turns, and then bound up. Got about 6 turns when I double
checked with a 5/16 24 bolt. I figured it was just garbage around the
set screw holes, so I made a set screw bushing to replace the pulley
with a 5/16 24 center taped hole in the middle. It went onto the end
of the ball screw about 4-5 turns and then bound up. I knew there
wasn't a problem with burrs on my bushing as I triple chased each hole
to make sure. The main bore and both set screw holes.

Finally just on a whim I whipped out a 5/16 24 die and it went a 7-8
turns onto the end of the ballscrew and started to jam up. Getting a
little frustrated I went ahead and ran it down. I can just barely see
the tiniest little double ridge under my pocket scope, but its a good
solid looking thread. No wrose than what a rolled thread looks like
under the magnifier.

I haven't a clue what thread it used to be, but its a 5/16 24 now.