Here beginneth the saga...
My Honda Rally 'adventure' bike (Tesco for the shopping and green-laning hereabouts) has a 'toolbox' which, with clever and astute packing will hold my jump-starter, OEM tool-kit (about as much use as a chocolate fireguard) and a bit and two bobs. Sorry Uncle
I decided it needed one of those 'hard man' tool tubes for £12 from Mr Zhang. It is the biz and everyone wants one.
It has a sealing 'O' ring to keep the shite out and at 1.5mm cross-section it was obvious it was going to fail at some point. So, back to Mr Zhang's relatives to buy some more to weigh down the tool tube even more. But what size?
If you have ever tried to measure the diameter of a large, floppy 'O' ring you will know it is like herding cats; push it in there, pull it out here, round a bit, no, not square a bit....
Eventually, two of my brain cells collided and I realised that measuring the diameter of the inside of the screw-on lid would give the diameter it had to 'stretch over' and that was the diameter I needed.
So, out with the shiny new super-dooper, highly accurate wotsit and it's in the bag. Measured twice for good luck so Mr Zhang's cousin won't make a loss on five large 'O' rings for £1:25 delivered.
120mm. Again, 120mm.
When they arrived they were way too big. You b'stad yellow-skinned theiving, cheating scoundrels.
Because there was no way in God's little green earth that I was going to send them back (£1:25 FROM China - £9:45 TO China), I cut one and spread it out and measured it and got that nice Mr. Pythagoras to work out the diameter. 120mm! I measured it again. 120mm. Now my finest Rabone steel rule may vary slightly between summer and winter and it has seen a fair bit of use down the decades, (not all of it for measuring stuff
) but it is as good as need be for this job.
So, out with the Aldi special. Zero it, wind it out to 120mm. It reads 120mm. Wind it back in, it says 15mm at zero. Zero it, wind it out to 120mm, it says 115mm. Wind it back in, 5mm. And so it goes on.
It isn't always wrong and not consistently either. Lets face it most builders have a steel tape with the first few inches missing but even they can compensate as long as more don't drop off while they are using it.
So, next time I'm passing, it's going back.
If I were using it for reloads I'd need a whole range of PPE to save me from the whizz bangs