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@Dave:
As I happen to use, just by chance,?a white tip variant of the pen which Erik uses I think I recognise it as a Papermate 0.7 mm Non-Stop Mechanical Pencil.

For you these maybe the easiest and cheapest to buy from the UK store as it looks an "international" variant of the Paper Mate:

The white tip variant is called a Paper Mate Sharpwriter and can be purchased in smaller quantities:
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So far for the "real stuff", as opposed to the, probably much better, touchy recommendations from Karl Jan
(I myself at least managed to destroy my mechanical pencil during an internal investigation, most likely not by ESD but due to overloading).
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What actually made me react on the topic is the point that this "Question" in itself shows that Erik is becoming a real star influencer on this forum.
Really hope he and we all benefit from this, because his tinySA is marvelous.

BenS