Glow Plug Nuts

I've just replaced a couple of glow plugs on my 200Tdi as the threaded end sheared off when I attempted to undo the nuts. For some inexplicable reason Beru can't see their way to including the tiny nut that clamps the ring connector to the glow plug and as the originals are seized onto the old plugs I can't reuse them. Any idea what size I should be looking for or where I can get them? My box of random nuts doesn't have anything small enough.

Thanks

I think they are M4 (?) if so ebay is your friend. Measure the diameter of the thread ....
https://www.ebay.co.uk/itm/M3-M4-M5...714207?hash=item362927e45f:g:KXwAAOSw63FaTUTG

They aren't all the same thread size across manufacturers I found
I also fitted beru and saved the old nuts but they didn't fit.
Unfortunately I can't remember what size the beru were.
Same issue when I got new brake flexi hoses and they came without nuts too. You can never save the old nuts off them!

Yes, I've had the same problem with the flexi hoses. You wonder how much it would cost them just to include the nuts! I'll get measuring. Thanks both.