Arma steel is a GM name for a malleable cast iron. Pontiac crankshaft for example were mostly cast, and are Arma steel. How many splines on the axle gears? What diameter is the ring gear bolt pattern?
A small part of the puzzle, appears to be a GM diff. https://www.thefreelibrary.com/Q+What+is+Armasteel?+Is+it+still+available?+If+not,+what+is+a...-a0175286114 Plugging in that second casting number shows 55-64 differential carrier series https://www.chevytalk.org/fusionbb/showtopic.php?tid/252789/
Came in a pile-o-parts in a clean out. Only part I couldn’t identify. Diameter isToo large for a Chevy,maybe Olds or Pontiac?
I don't think they are metric. If I remember right, they have a crazy marking because they are left hand thread. Gene.
Right. I just looked at mine, originally out of a '61 Corvette, has same markings. The one in question is a '64 piece.