OK, I have both a non-Helicomatic Maillard Atom Sport hub as well as a Helicomatic (500 I think) hub. I want to cannibalize the cones from the Helico for the Atom. Before I tear 'em both open, does anyone happen to know if the cones on these two models are interchangeble?

The left may be, but I'm fairly sure (allowing that it's been 30+ years) that the right one is smaller.

Memories mesh on this one.

The Maillard hub was bog-standard in the dim & misty, parts should be readily available & cheap.
A rummage in an old LBS should dredge up handfuls.

-Bandera

No. Both sides of most Helicomatic rear hubs use non-standard 5/32" balls, with the cones and cups to match that size. Standard hubs use 1/4" balls. There is apparently a "Sport" model Helicomatic hub that uses standard 1/4" balls, but I've never seen one in the flesh.

https://www.borgercompagnie.com/helicomatic/specs.html

OK, looks like John has solved the mystery. I'm not sure how to confirm if my hub is a 500 or Sport model, but if I remember right it's a 500, in which case I'm outta luck. Also if I recall correctly, I wasn't able to find cones for the standard Atom Sport hub, which seems odd given that it was a widely-used hub (wasn't it?) Shouldn't some LBS out there have a few of these in their bin?

You don't need an OEM replacement; you can use standard cones from e.g. Wheels Mfg. instead.

That's good news. My LBS led me to believe that I needed to source old Maillard cones for my Atom Sport hub. Anyhow, my old hubs will surely roll smoother with a new set of these in 'em. Thanks!

Sometimes you can find what you need on Ebay. I saved a Normandy Luxe Competition hub with a $5 Miche complete axle set.

The crucial measurements are the radius for the bearing race (to fit 1/4" balls) and the axle threading (10mm x 1mm for your Maillard hub). I'm thinking the most likely candidate would be this one:



Make sure the diameter (17mm) will fit through the hub dustcap. If the 13.8mm length of the cone differs significantly from the OEM cone, you should be able to compensate by adding or removing spacers. I wouldn't worry about a millimeter or two difference, though, unless it means your axle doesn't extend past the locknut.