Oops it's a left hand thread.

I have a few in stock for several different models. They break often , you could have remade the tensioner part it just would mean turning the screw backwards for tension..lefty tighty not righty tighty.
 
Having recently gotten a mill and lathe, I have been acquiring a lot of cutting tools, including several batches of assorted taps and dies from eBay. A friend called and asked if I could tap a 3/4 NPT in a well cap. After checking, I called back and told him yes, but the little voice told me something was off. I went back and checked again. There, very faintly, it said 3/4 NPT LH. To my eye, LH threads look very different from RH, and it had registered in my subconscious.

As for drawings, I took drafting and machine shop at the same time, along with working as an apprentice. Fred put me to work very quickly doing drawings (pencil and paper). I learned that the fewer calculations the machinist has to make, the fewer mistakes he will make. I ALWAYS dimension drawings for flat parts from the top left, as that is the way they will be worked in the mill, and never dimension between features unless tolerance dictates. Similarly, round parts are drawn with the small end on the right and dimensioned from that end. I've never felt it necessary to specify RH for a thread, but I can see that it might be a good habit to establish. I can't say I've ever had a machinist produce a LH thread when there was no call-out.
 
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