{"product_id":"swartchild-black-shield-mainspring-4391-for-16s-ingersoll-trenton-no-365-steel","title":"Swartchild Black Shield Mainspring #4391½ for 16s Ingersoll Trenton No. 365 - Steel","description":"\u003cp\u003e\u003cstrong\u003eSwartchild \u003c\/strong\u003e\u003cem\u003eBlack Shield\u003c\/em\u003e Mainspring #4391½ for 16s Trenton\u003cstrong\u003e \u003c\/strong\u003eand Ingersoll-Trenton Pocket Watches, Factory No. 365, steel, new in envelope. Could also very well fit in other watches as well. See images 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.\u003c\/p\u003e","brand":"Swartchild","offers":[{"title":"Default Title","offer_id":48929980055860,"sku":"PMA-SWA4391S-10","price":6.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0849\/3341\/1124\/files\/2025-10-28_17.20.56.jpg?v=1761697577","url":"https:\/\/www.vintagetimeparts.com\/products\/swartchild-black-shield-mainspring-4391-for-16s-ingersoll-trenton-no-365-steel","provider":"Vintage Time Parts","version":"1.0","type":"link"}