L'assale dovrebbe essere in alluminio, il corpo cassetta lo fanno sia in acciaio che in alluminio...
Ho fatto una breve ricerca su evvay, ed ho trovato un'immagine chiarificatrice dell'Heavy Duty (che non mi fa allegare anche se è di soli 40K), e questa descrizione:
Heavy Duty
When you need that extra toughness, this Full Heavy Duty hub will deliver, and it's a great bargain as well. Included is a heavy duty, bolt-on axle, fun bolts, stainless steel drive shell, and the necessary lock-collar axle clamp. Bought separately, just the upgrade parts alone would cost well over $200.00. When you buy this Full Heavy Duty hub from us, it costs only $80.00 more than the comparable, standard duty hub. This hub fits standard road, cross, or mountain bike dropouts, so you can upgrade from quick-release to Heavy Duty Bolt-On with no modifications to your bike.
Ah, il peso dichiarato per il solo mozzo posteriore Heavy Duty è 346g.