Homemade tap

[DogBunny]

As an industry standard, it was about 99.9% universal...... 'till the fuckin' Chinese started making anything and everything. They decided it weren't that important. I've got dozens of old acetylene gauges, fittings, regulators and torches. All of 'em ancient and predate the Chinese's penchent for makin' cheap shit. Every single one has the left hand thread groove cut in 'em.
If you have a nut, bolt, fitting or widget of any kind that's left hand thread and doesn't have the groove... I'll lay ya odds it's Chinese.

Surely true. Not trying to aggravate, just stating what's out there... A Google image search of "left-hand nut" shows probably less than half are grooved. One I saw is stamped LH, no groove. Some have arrows, no grooves.

According to the above one-minute video, posted by a FASTENER SUPPLIER, NO LESS, the ONLY way you can tell is by the arrow.
The nut on my motor arbor has nothing.

 

[Jim]

Well like I said, at one time it was almost universal... not so much anymore huh...
Here's a turnbuckle barrel. Most of y'all know what a turnbuckle is. the cable ends screw into the barrel. One end is normal and the other end is reverse threads so that, as you screw it in, it pulls the cable tight. Guess which end has the left hand threads?

 

[bosco659]

For oddball taps I’ve found Amazon can be your friend.

 

[Mikey]

I never knew that, thanks.

View attachment 332018
Aside from Yamaha mirrors, the only thing I have that I can think of that is left-handed is the extended arbor on my motor for my grinder/buffer/ wire wheel. Left hand nut, but it's plain, no grooves.
Just thought of another -- gas fittings are left-handed so you can't accidentally cross them with oxygen lines. Looking at images on Google, many lefty gas fittings are grooved, but not all.

I have the same setup on my bench grinder ones LH and ones RH
I'll look later but I'm sure it came from China so probably no groove on the LH