{"product_id":"chevy-12-bolt-billet-main-cap","title":"Mark Williams 58100 Billet Steel Main Cap Black Oxide — Fits GM 12-Bolt Differentials","description":"\u003cdiv style=\"background:#f7f7f7;border-left:4px solid #c00000;padding:14px 18px;margin:0 0 18px;\"\u003e\n\u003ch3 style=\"margin:0 0 6px;font-size:1.1em;\"\u003eAbout Mark Williams\u003c\/h3\u003e\n\u003cp style=\"margin:0;font-size:0.95em;line-height:1.55;\"\u003eMark Williams engineers high-quality automotive parts and accessories trusted by enthusiasts and shops across North America. At GGCRACING we stock the full Mark Williams lineup with fast shipping and expert fitment support — order with confidence.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003ch2\u003eStrengthen Your GM 12-Bolt Differential with Mark Williams Billet Main Caps\u003c\/h2\u003e\u003cp\u003eFor high-horsepower applications and extreme racing conditions, stock differential main caps often fall short. The Mark Williams 58100 Billet Main Caps are engineered to provide unparalleled strength and rigidity to your GM 12-bolt differential. Crafted from premium billet steel and finished with a durable black oxide coating, these main caps prevent cap deflection, ensuring consistent gear mesh and extending the lifespan of your differential under severe loads.\u003c\/p\u003e\u003ch3\u003eUncompromising Strength \u0026amp; Precision\u003c\/h3\u003e\u003cp\u003eMark Williams is a name synonymous with drag racing excellence, and these main caps embody that reputation. Designed to withstand the most demanding environments, they are a critical upgrade for any serious performance build.\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cb\u003eBillet Steel Construction:\u003c\/b\u003e Machined from solid billet steel for maximum strength and resistance to flex.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eBlack Oxide Finish:\u003c\/b\u003e Provides corrosion resistance and a stealthy, professional appearance.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eHardware Included:\u003c\/b\u003e Comes complete with all necessary hardware for a straightforward installation.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eEnhanced Rigidity:\u003c\/b\u003e Prevents main cap walk and deflection, maintaining optimal gear alignment under extreme torque.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eDirect Fit:\u003c\/b\u003e Specifically designed for GM 12-bolt differentials, ensuring precise fitment and performance.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eThe Foundation for Extreme Performance\u003c\/h3\u003e\u003cp\u003eUpgrading to Mark Williams billet main caps is a fundamental step in building a bulletproof GM 12-bolt differential. By reinforcing the carrier bearing bores, you mitigate one of the weakest links in a high-performance rear end, allowing your differential to handle more power and abuse without failure. This investment translates directly into improved reliability and consistent performance on the track or street. Secure your drivetrain's future with Mark Williams quality from GGCRACING.\u003c\/p\u003e\n\u003cdiv style=\"margin:24px 0;border-top:1px solid #eee;padding-top:18px;\"\u003e\n\u003ch3 style=\"margin:0 0 6px;\"\u003eOften bought with\u003c\/h3\u003e\n\u003cp style=\"font-size:0.9em;color:#555;margin:0 0 8px;\"\u003eOther popular Mark Williams products customers consider together:\u003c\/p\u003e\n\u003cul style=\"padding-left:20px;margin:0;\"\u003e\n\u003cli style=\"margin:4px 0;\"\u003e\u003ca href=\"https:\/\/ggcracing.com\/products\/quick-rel-steering-hub\" style=\"color:#0066cc;text-decoration:none;\"\u003eMark Williams Quick Release Steering Hub 3\/4in Shaft — 4-Bolt Wheel\u003c\/a\u003e\u003c\/li\u003e\n\u003cli style=\"margin:4px 0;\"\u003e\u003ca href=\"https:\/\/ggcracing.com\/products\/gt-5-bolt-quick-release\" style=\"color:#0066cc;text-decoration:none;\"\u003eMark Williams GT 5-Bolt Quick Release - Grant GT 3\/4in Shaft — Black Anodized Aluminum\u003c\/a\u003e\u003c\/li\u003e\n\u003cli style=\"margin:4px 0;\"\u003e\u003ca href=\"https:\/\/ggcracing.com\/products\/q-r-steering-hub-6-hole-sparco-momo-str-wheels\" style=\"color:#0066cc;text-decoration:none;\"\u003eMark Williams SFI 42.1 Quick Release Hub — Fits Sparco\/Momo 6-Hole\u003c\/a\u003e\u003c\/li\u003e\n\u003cli style=\"margin:4px 0;\"\u003e\u003ca href=\"https:\/\/ggcracing.com\/products\/gm-8-5-10-pinion-yoke\" style=\"color:#0066cc;text-decoration:none;\"\u003eMark Williams 1350 U-Joint Pinion Yoke — GM 8.5\" 10-Bolt, 30 Spline\u003c\/a\u003e\u003c\/li\u003e\n\u003cli style=\"margin:4px 0;\"\u003e\u003ca href=\"https:\/\/ggcracing.com\/products\/th400-t-10-trans-yoke\" style=\"color:#0066cc;text-decoration:none;\"\u003eMark Williams TH400 T-10 Slip Yoke 32 Spline — 1350 U-Joint\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cscript type=\"application\/ld+json\"\u003e{\"@context\":\"https:\/\/schema.org\/\",\"@type\":\"Product\",\"name\":\"Mark Williams 58100 Billet Steel Main Cap Black Oxide \\u2014 Fits GM 12-Bolt Differentials\",\"description\":\"Reinforce your GM 12-bolt differential with Mark Williams 58100 billet steel main caps. 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Contact our experts at GGCRACING with your VIN and we'll verify before you order.\"}},{\"@type\":\"Question\",\"name\":\"How long is shipping for Mark Williams?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Most in-stock items ship same or next business day. Free shipping on orders over $99 in the continental US. Tracking is provided via email as soon as your order leaves our warehouse.\"}},{\"@type\":\"Question\",\"name\":\"How do I install the Mark Williams 58100 Billet Steel Main Cap Black Oxide \\u2014 Fits GM 12-Bolt Differen?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Most installs are bolt-on with basic hand tools. See manufacturer documentation for torque specs and procedures.\"}}]}\u003c\/script\u003e","brand":"Mark Williams","offers":[{"title":"Default Title","offer_id":40881385865300,"sku":"BJFM_58100","price":108.0,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0552\/3210\/2484\/files\/MWE58100.jpg?v=1714535375","url":"https:\/\/ggcracing.com\/products\/chevy-12-bolt-billet-main-cap","provider":"GGCRACING INC","version":"1.0","type":"link"}