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any one in particular that's tester approved?
All the generic ones are about the same, surprisingly good and as good as you need for most bicycle stuff. Whatever is on offer in your favourite shop is fine. Mine looks a lot like this, apart from being 200mm for reasons connecting with my use of Zipp VumaChrono cranks, 150mm is sufficient for normal people.
If you want to measure accurately, you need a micrometer, of which the #tester_approved 0-25mm variant is a Mitutoyo 102-707, but that's way more tool that you need for bike stuff.
any one in particular that's tester approved?