Short version:
Stub-Twist was made with higher quality iron; horse-nail stubs mixed with coach spring steel, fused ("puddled") into a "bloom of iron", then hammer forged into rods, rolled into threads but
NOT twisted, which were then wrapped around a mandrel and hammer welded.
Long version: spend the weekend looking around here
http://docs.google.com/Doc?id=dfg2hmx7_186fpmvhzsb