I have one Atax seatpost - the only one I've ever seen, in fact. This one is clearly dated "01 1986" and is a common French diameter of 26.4 mm. It is also appropriately short; from the days when people actually still rode bikes in frame sizes to match their leg length. Shaft is 145 mm with short flutings (between 5 and 50 mm from the top). Weight is 240 grams.
The top of this one then tapers into a wide and uncommonnly thin "blade" at the top, and without the saddle mounting hardware it might look like an ice scraper for your windshield. A single 6mm cap head bolt enters from below and threads into the alloy cradle top. What is unique about this post is the lower cradle which is a broad piece of black plastic which follows the curve of the top of the forged post.
It looks simple, even cheap - both because of the black plastic piece and also because of numerous little "v"s stamped or cast onto the alloy which direct your eyes rearward toward a measuring guide - marked form 0 to 6 cm, above the limit line. The shaft is bored through to the top and is plugged with a bit of bees wax... This may have been added later, but I suspect it was original.
To my surprise, although not the most attractive post, it actually holds a saddle very securely. I thought that surely the black plastic plate would easily slip atop the wide smooth alloy wedge of the post-top, but it does not.
I'm not sure how Chris's or any other Atax posts compare, but this piece at least, is a perfectly decent, albeit less than elegant, seatpost. And, this one was made for an increasingly hard to fit classic "French" seat tube dimension, so I can't complain. Besides, it was tossed in with a French 1970s frameset I'd bought a while back, so it cost me nothing. Whadda deal!
Bob Hanson, Albuquerque, New Mexico, USA