Newall Security Mainspring #710 for Howard 12s Factory No. 553 - Steel

Newall Security Mainspring #710 for Howard 12s 17 to 21j movements, Factory No. 553, T-end, steel, new in envelope. See image for further details. I likely have several of these so the one you get may differ slightly from the images. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.