Swartchild Black Shield Mainspring 4402 or 16s E. Howard Factory No. 55 - Steel

Swartchild Black Shield Mainspring 4402 for 16s "L" size E. Howard, or OLD Howard, Factory No. 55, steel, new in envelope. See images for further details. Be aware that Howard marked both the 18s and 16s as a P/N 55, which certainly makes no sense, but the third image correctly shows the difference. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do an adequate but perhaps somewhat incomplete job of representing the item.