The Staedtler Chinagraph is the most common mechanical chinagraph I've seen, but have always been prone to breaking.
If you can get the
refills then get an artist's 3mm clutch pencil and use the chinagraph leads in it, much nicer. At the risk of outing myself as a pen freak, my favourite (using Staedltler leads) chinagraphs are the
Lamy Scribble and the
Copic Nobby