Vernier caliper pens

Vernier caliper pens

Small silver plastic bodied pens with a small vernier caliper to the side. 

These are not precise tools; please don't expect to be able to accurately tell the difference between 5.8MM and 6MM using them.

Personally I'd say they're good enough to tell the difference between 5.5 and 6.0MM though, which is sometimes all you really need from a cheap pair of pocket vernier calipers. 

The ink is blue and they do write quite nicely, although the pen feels a little odd in the hand due to the shape. I can't say how long the ink will last, or whether you can get replacements, though.