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I haven't got a set of callipers, but measured the shell as 69mm wide x 37mm diameter.
The frame is a Davanti, which as far as I know is a generic alloy frame branded by a bike shop here in Holland.
The bb says BB-7420, BC1.37x24T, 68. It's sold as "FSA RPM JIS Square Taper Bottom Bracket BB-7420AL BSA-68-ST"
I've added a photo of the threads as well.
1 Attachment
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Kgrev
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Pretty sure you have an Italian threaded bottom bracket shell.
It's long been common for Dutch shops to source the bikes they re-brand from Italian builders.
If you had calipers, I think you'd find that your shell measures 70mm x 36mm and the DS has a right-hand (ie "normal") thread, rather than the left-hand thread you find with British/ISO BB.
As the BB you have is British the diameter is less, so the cup falls through the shell.
Why does the NDS engage? Manufacturing tolerances I'd guess: it screws in, but I bet it's pretty loose.
What you need is an Italian threaded BB: instead of "1.37x24T", look for "36x24T". If a BB isn't specifically listed as "Italian", then it's likely "British".
Have a look a Sheldon's cribsheet for more info: the table at the bottom shows you what happens if you mix the wrong shell and BB.
Scilly.Suffolk
The frame isn't French or Italian is it? Actually, what is the frame?
Start from scratch: (accurately) measure the width and diameter of the shell, then post the details here together with what is written on the bottom bracket.
It's not easy trying to diagnose things remotely: no details and no photos just make it even harder.