I've always been a big fan of writing instruments, and since I work in the architectural field, I have built up a decent collection. While reviewing my collection, I counted 4 of the tools I use are from Rotring 600s collections and realized that I am happy to have these exact irreplaceable tools: pen, ballpoint, and two 0.7 mm thin line mechanical pencils - one has a silver finish and the other matte black.
I have had the original Rotring 600s collection tools since 2003 and I bought them in the National Bookstore (London, UK). The greatest beauty in these tools is that they look like old precise drawing tools.
The original design was recently stopped and replaced by a series of Rotring 600 Nm, but from many reviews that I have read, and from personal experience, I think that the original 600s series tools are much better designed (no surprise, because the price is now on eBay U.S. $ 50 or more).
In addition to its solid construction the unique feature of the hexagonal, solid brass body of the barrel pen is the diamond-cut, knurled grip giving it the appearance of a precision tool. And it is a precision tool. I especially like that they are heavy - making it easy to hold the pens steady.