I have a E18-D80NK sensor, and it has a variable resistor type adjustment on it. Some variable resistors have a limit, one way or the other. Presumably this one does as well. The issue is that you can turn it multiple times, and I am yet to reach a point where it stops turning, and locks.
I presume that when you wind it in clockwise, it will eventually stop, and lock position. What I am really asking is whether it can be wound out so far that it detaches or something?
Usually, there is a lock somewhere. Where it will not move further.
Unless you use excessive force.
That will damage your stuff.
Multi turn resistors are usually up to 10 full turns.. .
If you can turn it more than 10 full turns it is either a pretty special one or it is broke...
That puts my mind at ease, thank you. I will try winding it all the way in and use no excessive force. I have worked out at least that winding it in increases the sensor distance detection.
Is this the yellow bodied, black headed sensor on AliExpress at £1 (approx)?
I couldn't see where you adjust it, but frankly, at that sort of price, you aren't going to get a lot.
A multi-turn potentiometer, the type with a body and 1/4" shaft, pretty expensive, wire wound, will have stops, as will the lead screw types.
On this sort of item, as in PIR motion sensors used for lighting or burglar alarms, they tend to use 270 degree singe turn pots with stops.
I must admit I have never seen one of these setting pots without stops. Maybe they haven't bothered.
They are a bit more than that on Amazon. Prices range from more like 6 AUD, so about 3 pounds in UK money. It is what you described though. Black head and yellow body. Some of the prices seem really a lot higher than others, by even double or more.
This is what Google Ai says:
The sensor has an adjustable range of approximately 3 cm to 80 cm. You'll need to rotate the screw several times to cover the full range, as it's a multi-turn potentiometer.
Thank you Wawa. I found that when I wound it in, clockwise, too far it was unresponsive to anything. I also found that it did not stop, but I think there was a clicking sensation, like it had actually reached the end of the threads. I was worried then because I thought I may have wound too far. It seems to have an optimum range of about half a meter, and was seemingly not so responsive when I tried to get it to 80cm, like it says on the specifications.
There are also pots with a linear resistance lane. And a taper that is on a long screw, that moves it along the lane. Those may have plenty turns...
And are cheaper than the spiral ones....
It depends on the reflecting surface and angle of the sensor.
That is a good point. I noticed that when playing around with it.
£0.49 on AliExpress this morning.
Too good to be true.
Be aware that some multi turn pots are clutched, so you can keep turning but the wiper doesn't move any further.
You can sometimes hear a faint click when the end of travel is reached.
I got a a very faint clicking sound when I continued going further clockwise. It is not worth getting that far in anyway because it becomes unresponsive after you wind it in too far.
Hi, @extant4life
FIRST important questions.
Tom.... 
PS 12 posts!!!!!!!!!!!!!!!!!!!!!!
Not so sure I want to open it up and start digging about inside the unit tbh. Thank you for the tip, but that seems more like something for a discreet component that you might be about to use on a project. I should be ok with it, because if I wound it in too far it stops switching off and on anyway 
Multi-turn pots are able to take some abuse past their end stop.
Why do you think you have a problem. Maybe there is no problem.
Leo..
Thanks, no there does not seem to be a problem now. Just wanted to check before I started adjusting it. Now I know, I can be happy with adjusting any similar things in the future. I should really mark one as solved, but so many to choose from. I will just do the first response… gratz build_1971 
Hi, @extant4life
You should be able to check it in circuit, for when the pot approaches each end.
An image of the pot would help.
Tom....
How will you know it will be similar?
Better than an image would just be to look at the datasheet I think, E18-D80NK. It seems like a very commonly used one. I have not seen one on any site that looks different style to the one I have. It is a nice little bit of kit I think, but very variable in price for some strange reason. I tried to find details on adjusting it but didn’t find much. The advice on here has been good.
Hopefully by appearance, but I am still learning. Hopefully quite fast. And also, I did have some other variable resistors with a kit I bought. They seem to turn only less that 360 degrees. I noticed this was different because it did not stop, but just kept winding, and it was still changing the sensing distance. Then I realized that there are quite a few different types.