{"product_id":"swartchild-black-shield-clock-mainspring-4-0-x-30-mm-x-28-ref-40-30-b-72","title":"Swartchild Black Shield Clock Mainspring 4.0 x .30 mm x 28½\" Ref 40-30 B 72","description":"\u003cp\u003e\u003cstrong\u003eSwartchild \u0026amp; Co \u003cem\u003e\u003c\/em\u003e\u003c\/strong\u003e\u003cem\u003eBlack Shield\u003c\/em\u003e\u003cstrong\u003e\u003cem\u003e\u003c\/em\u003e\u003c\/strong\u003e Clock Mainspring, OPEN LOOP End, GR Ref. 40 - 30 B 72, steel, new in envelope. See images for precise mainspring specifications. I specialize in hard to find watch \u0026amp; clock parts and all parts are unconditionally guaranteed. Images do a pretty good job of representing the item\u003c\/p\u003e","brand":"Swartchild \u0026 Co","offers":[{"title":"Default Title","offer_id":48622132396340,"sku":"CMS-SW4030B72S-05","price":6.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0849\/3341\/1124\/files\/2025-06-1219.56.04.jpg?v=1749783561","url":"https:\/\/www.vintagetimeparts.com\/products\/swartchild-black-shield-clock-mainspring-4-0-x-30-mm-x-28-ref-40-30-b-72","provider":"Vintage Time Parts","version":"1.0","type":"link"}